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Four digit phone numbers 2014-02-25
From Tom:
Hi, I'm an online math teacher, working on lessons for my students.

This question is in their book and I can't do it...! Help!

It has to do with phone numbers, and in this problem, we are only dealing with the last 4 digits of the number.

It asks how many possible numbers we have if at least one digit repeats in the last 4 digits of the number.

Answered by Penny Nom.
A number with all the digits different 2014-02-07
From Jon:
I'm not a mathematician but just curious. Is there a name for a number of up to ten digits where each digit is different, i.e the equivalent of an isogram in linguistics? My online banking gives me a random 8-digit number each time I log on and it is rare to get one of the type I refer to. There must be calculable odds, but I'm only allowed one question!
Thanks in advance
Jon

Answered by Harley Weston.
A 4 digit number 2013-12-20
From swathi:
How many 4 digit numbers can be formed using the digit 3 only once but the digit 3 must be used in all numbers?
Answered by Penny Nom.
A 2-digit number 2013-05-13
From A teacher:
Find a “2-digit number” where the sum of the 1st digit (on the Left) and the square of the 2nd digit equal the same number.
Answered by Lorraine Dame, Harley Weston.
A 4 digit code 2013-03-26
From chris:
I saw a previous question about a 4 digit code type thing and I was wondering if you could email me that same type of thing. I changed the pin number on my phone's lock screen and I tried hard to remember it, then I had to go help my mom with something and I automatically forgot it and there is no way for me to get back on my phone. I need all of the possible 4 digit number combinations without the numbers 0, 1, or 2. It cannot be repeating, ascending, or descending.
I know you may not want to do all of them, but I really need it.

Answered by Robert Dawson.
A 3 digit number puzzle 2013-03-11
From Bonnie:
My number has 3 digits. My number is not a multiple of 100. My number is a multiple of 50. My number is a factor of 1000. What is my number?
Answered by Penny Nom.
Four digit "combinations" using 0124 2013-02-27
From Ayana:
What are all the possible four digit combinations using 0124. Please list them for me. Thank you.
Answered by Penny Nom.
A 4 digit phone lock using the digits 4, 2, 3 and 0 2012-12-24
From Ragu:
I would like to know formula for searching a combination of 4 digit. eg.

I knew my Phone Lock combination is my car plate number 4230. But this time, i used another way around instead of 4230.

But I am sure, there is only this 4 digits only. 4 & 2 & 3 & 0

Answered by Penny Nom.
The last 4 digits of a cell phone number 2012-12-22
From Jacob:
If the last 4 digits of a cell phone number, XXX-XXX-ABCD, are restricted where: A cannot be 0 or 1 and B cannot be 0 / how many possible 4 digit combinations are left?
Answered by Penny Nom.
Some 6 digit numbers 2012-10-23
From Mason:
How many different 6 digit numbers can you make using the digits 1 ,2 5, 6, 7, and 9? How many of these six-digit numbers are divisible by 6?
Answered by Penny Nom.
4 digit combinations 2012-10-17
From Scott:
How many different 4- number combinations from 0-1-2-3-4-5-6-7-8-9 with 2 out of the 4 odd and 2 out of the 4 even, with no numbers repeating. Thanks
Answered by p.
A 2-digit number 2012-08-23
From patty:
Write the 2-digit number that matches the clues. My number has a tens digit that is 8 more than the ones digit. Zero is not one of my digits. My number is
Answered by Penny Nom.
A 4 digit number 2012-08-09
From May:
The number is given as ABCD. The first digit is a quarter of the last digit. The second digit is one less than the first digit. When the number ABCD is multiplied by four its digits appear in the reverse order. None of the digits are the same. What is the number. Pleas help because my child need help and I can not do this. Thank you.
Answered by Penny Nom.
Mr. Schneider's mass 2012-02-29
From Khiya:
Mr. Schneider's mass is 2 digits. The first digit is 3 times the second digit. Both digits are odd numbers, and his mass is greater than 35 kg. What is Mr. Schneider's mass?
Answered by Penny Nom.
Can the result of the calculation be 2? 2012-02-09
From Thomas:
You have the digits 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9 in a random order side by side and put randomly between two digits a colon, so that a division comes into existence. Can the result of the calculation be 2?
Answered by Robert Dawson and Chris Fisher.
A two digit number 2012-01-29
From Christine:
Five times the sum of the digits of a two digit number equals the number. If the digits are reversed, it becomes nine more than the original number. What is the original number? I really don't understand this question, help me please
Answered by Penny Nom.
The number of digits in a number base m 2011-12-22
From Jash:
Assume there is a number system of base m.

The one property of this system is: If 2 numbers written in this system, which have 'a' and 'b' as the number of digits are multiplied, then the product of the 2 numbers will have a number of digits which is a function f(a,b).

In other words, as long as the number of digits of the 2 numbers are constant, the number of digits of their product is a constant.

Find m.

Answered by Robert Dawson.
Rounding 2011-12-14
From seth:
A decimal number rounded changed to 23.7 after it was rounded. Give a decimal number that is less than 23.7 and another that is greater than 23.7 that each round to 23.7. Explain to what place each number was rounded.
Answered by Penny Nom.
3-digit, daily numbers 2011-09-29
From Margaret:
I need the list/group for a raffle that would contain the combinations for a 3 digit (000-999) daily number. There would be 100 tickets sold with 10 3-digit numbers from each numerical group beginning from 000's, 100's 200's, 300's,...900's. No duplicates/replacement. What would be the list of possible combinations of each group of 100 tickets, keeping each different group/list of combinations in separate blocks of 100 tickets without duplication. So I could use 1 list of 100 this year and the next list of combos next year and so forth. Please help!

Example: 000,197,245,367,445,569,618,777,842,964

What would be the possible lists of each 100 tickets? Thank you

Answered by Penny Nom.
A number less than 100 2011-09-17
From Sharon:
I am a number less than 100. My ones digit is 6 the sum of my digit is 11. What sum am I?
Answered by p.
A four digit number 2011-09-16
From gina:
i am having a hard time figuring this out.. i believe the answer is 3105 but the 0 is throwing me off... i am a 4 digit number between 3100 and 3200, none of my digits are even, the sum of my digits is 9, the largest digit is in the ones place, what number am i ??
Answered by Penny Nom.
A two digit number 2011-08-26
From Felicia:
Write the 2-digit number that matches the clues.
My number has a tens digit that is 8 more than the ones digit.
Zero is not one of my digits

Answered by Penny Nom.
What is the 6001st digit that Sam wrote? 2011-02-15
From Sarah:
Sam wrote the natural numbers from 1 to 5280 in order. What is the 6001st digit that Sam wrote?
Answered by Penny Nom.
Reversing the digits 2011-02-08
From rejie:
if the digits are reverse , the number is 9 less than the original number.what is the equation?
Answered by Penny Nom.
Four digits are to be randomly selected 2011-01-20
From sarahbear:
Suppose four digits are to be randomly selected (repetitions allowed) Find the probability that
A. 5562 is selected
B.0000 is selected
C. All four digits are the same
D. 2 is the first digit selected

Answered by Penny Nom.
A product of 1 000 000 2010-11-19
From Sharron:
There are many pairs of numbers that when multiplied together give a product of 1 000 000. However, there is one pair, and only one pair, of whole numbers that contain no zero digits and has a product of 1 000 000. What are these two numbers?
Answered by Stephen La Rocque.
What numbers can I be? 2010-11-13
From john:
my thousands digit is 2 times my ones digit.my hundreds digit is my ones digit plus 2. my tens digit is the difference between my thousands and hundreds digit what numbers can i be?
Answered by Penny Nom.
Choose any three digits that are less than ten 2010-09-12
From cecille:
my son have a homework, but i don't understand the question. here's the problem:
choose any three digits that are less than ten.
make all the two digit number you can using those three digits.
add up the two digit numbers you created and divided by the sum of the original three digits.
record your answer. then do it again with another three digits. write your observation about the answer.

Answered by Claude Tardif.
Numbers that can be formed using the digits 1,2,3,4,5,8,9 2010-07-19
From Donessa:
write the number that is 2000 more than the difference between the largest and the smallest number that can be formed using the digits 1,2,3,4,5,8,9
Answered by Tyler Wood.
Two problems 2010-05-27
From debbie:

Question from debbie, a parent:

hi, i have a daughter and she asked me a maths question I cannot solve. I was just wondering if you can give me the answers plus the working out so I could explain to my daughter,

1. The leftmost digit of a six-digit number N is 1. If this digit is removed and then written as a rightmost digit, the number thus obtained is three times N .Find N.

2. Four friends are racing together down a flight of stairs. A goes 2 steps at a time, B 3 steps at a time. C 4 steps at a time and D 5 steps at a time. The only steps which all four tread on are the top one and the bottom one. How many stairs in the flight were stepped on exactly once?


Answered by Penny Nom.
Four digit numbers 2010-05-22
From tyeisha:
Whats all the four digit numbers you can come up with using numbers 0-9
Answered by Tyler Wood.
Odd numbers with no repeated digits 2010-05-01
From jameka:
How many odd numbers can be written from the set {2,3,4,5,6} if no digits may be used more than once?
Answered by Penny Nom.
How many zeros? 2010-03-18
From jeff:
1 light yr is 6,500 billion miles, the galaxy "Andromeda" is 2,500,000 million light yrs, how many zeros are in this equation ?
Answered by Robert Dawson.
A code on my pedometer 2010-02-19
From Jacqui:
Hi I need to break a code on my pedometer. I have only 3 digits 1 2 and 3 but need to fill a 5 digit code. I have tried to find answers but they seem to relate to if the digits are only used once. I can use them in any order and repeated as many times. How many possibilities are there and is there an easy way to run through them. Many thanks
Answered by Tyler Wood.
4-digit positive numbers 2010-02-15
From marjon:
Find the sum of all the 4-digit positive numbers with no zero digit.
Answered by Penny Nom.
Three digit odd numbers 2010-02-04
From Rebecca:
Question from rebecca, a student:

how many three digit odd numbers can be formed using the digits 1,2,3,4,5,6 without using any digit more than once?

Answered by Tyler Wood.
A 4-digit phone code 2010-01-21
From pat:
my daughter can`t remember her 4-digit code to unlock her phone. she is pretty sure it starts with a 4. can you help us? my brain is locked up
Answered by Robert Dawson.
A place value problem 2009-11-29
From Ivy:
My tens digit is 4 less than my thousands digit. My ones digit is twice my tens digit. My ten thousands digit is one less than my ones digit. My hundreds digit is the sum of my tens and thousands digit. My thousands digit is 6.
Answered by Penny Nom.
Jill and Bill 2009-11-04
From Lisa:
Jill and Bill are two members of the Hill family. Jill is 8 years old and Bill is 9 years old. What will Bill's age be when the total of the digits in both their ages is once again 17?
Answered by Stephen La Rocque.
In what order are the following digits? 2009-09-30
From Jewell:
In what order are the following digits? 0,2,3,6,7,1,9,4,5,8
Answered by Penny Nom and Claude Tardif.
The sum of digits of 4444^4444 2009-08-31
From SHIVDEEP:
The sum of digits of 4444^4444 is A .The sum of digits of A is B .
Find the sum of digits of B ?

Answered by Claude Tardif.
Unlocking my suitcase 2009-08-21
From Jamboree:
I need to have all the possible combination of three digit between 0-9, i have seen the answer that there are 720 combination are there. Could you please show me all those combination numbers so that i could try it out to unlock my suitcase, will you please write it down all those combination and send it to me
Answered by Victoria West.
A number puzzle 2009-05-17
From Gita:
Ok, we really need help for a homework problem due on Monday morning
I've been trying for 2 hours and can't figure it out---if I can't I'm not sure
how my son can....We've been given a puzzle with the following rules:
--The sum of each side must equal 15
--We can only use the numbers 1,2,3,4,5,6,7, 8
--A number can be used only once
(Hint: Think of all combinations of 3 numbers = 15)
--The puzzle looks like this:

_____ _______ ______

_____               ______

_____ _______ ______


Answered by Penny Nom.
7 digit combinations 2009-05-11
From CAROL:
I NEED TO KNOW HOW MANY 7 DIGIT COMBINATIONS FROM 0-9 THERE ARE WITHOUT ANY REPEATES, OR WHAT THOSE COMBINATIONS ARE?
Answered by Penny Nom.
Combinations and permutations 2009-05-07
From Renee:
We are trying to figure out the equation or how to solve the problem of how many combinations of 4 digits you can get out of 0-9 without repeating the numbers in a set (i.e., no 0001, 0002) begining with 0123, 0124, 0125 etc Thanks!
Answered by Stephen La Rocque.
Four-digit combinations 2009-04-18
From Carri:
How many 4-digit combinations can be made out of digits 1, 2, 3, 4, & 5 using each number once? What are the combinations?
Answered by Penny Nom.
How many times is 9 in pi? 2009-04-09
From Serena:
How many times is 9 in pi?
Answered by Robert Dawson.
A 5 digit push combination lock 2009-04-04
From Andrew:
I have a 5 digit push combo lock that i forgot the combo for. it has numbers 1-4 and each number can be pressed more then once ie. 11111, 36356 is there an algorithm out there that will list out the possible combinations for me? or maybe a way i could write them out myself.
Answered by Penny Nom.
0123456789 2009-03-25
From Dr.:
Many years ago I discovered that there are 33 numbers which, when multiplied by 0123456789, simply rearrange the digits. Surprisingly (to me at least) is the fact that the digits of all of those 33 numbers add up to one of the 6 "cardinal" numbers 1, 2, 4, 5, 7, and 8. For example 6 + 2 = 8 and 62 X 0123456789 = 7654320918 etc.
Another interesting (to me) fact is that only the cardinal numbers 1, 2, 4, 5, 7, and 8 rearrange the digits in the number 9876543210.
My question is: "Is this known to anyone but me and the people I have told?"

Answered by Robert Dawson.
4 digit numbers from 1159 2009-03-10
From David:
I have the digits "1159" and need to come up with a complete list of possible four-digit combinations. It does NOT matter the order of the two number ones (1), so this will help eliminate many possibilities.

Separately, it would also help to actually know the actual number of combinations with which I am dealing to start.

David :)

Answered by Penny Nom.
Four digit numbers 2009-03-10
From Theresa:
I need to know the number of 4 digit numbers that can be formed using 1-2-3-4 without repeating numbers
Answered by Penny Nom.
4 digit strings starting with 7 2009-03-03
From Angel:
I need to no all the 4 digit combinations starting with 7 and with no repititions.
Answered by Penny Nom.
The page numbers in a book 2009-02-10
From Nichole:
It takes 852 digits to number the pages of a book consecutively. How many pages are there?
Answered by Penny Nom.
Dividing the digits 1 - 9 into two groups 2009-02-09
From donna:
using the numbers 1 to 9 can you arrange these into 2 groups, both of which have the same total, and no you cant turn the 6 upside down
Answered by Penny Nom.
4 digit arrangements of 7 3 6 6 2009-02-05
From Carole:
I need all the four digit combinations using the numbers 7 3 6 6
Answered by Penny Nom.
Missing three digits in a phone number 2009-01-30
From Elmer:
I have part of a phone number. the first 3 digits are 212, the last digit is four, and the three missing digits are all odd, how many numbers will I have to call to get the right number?

212- _ _ _ 4?

Answered by Stephen La Rocque and Penny Nom.
Four digit numbers using 1, 0, 2 and 8 2009-01-27
From Mike:
How many combinations of this four digit number 1028 can this produce only using those numbers. Example would be 0000, 0001,0002,0008,0010,0011,0012,0018,etc...
Answered by Penny Nom.
Three consecutive natural numbers 2009-01-26
From abby:
1.what is the smallest four-digit number that is the sum of the three consecutive natural numbers? what are the three consecutive natural numbers that give this sum?

2.what is the largest three digit number whose square root is a prime?

Answered by Penny Nom.
The tens digit of 0! + 1! + 2! + 3! + 4! .............+9999! + 10000! 2009-01-23
From Kaylyn:
determine the tens digit for the expression:
0! + 1! + 2! + 3! + 4! .............+9999! + 10000!

Answered by Robert Dawson and Penny Nom.
A three digit number 2009-01-20
From marcha:
when this three digit number is rounded to the nearest ten, the sum of its digits is 16 the hundreds digit of this number is 8 and the ones digit is 5, what is the number?
Answered by Robert Dawson.
A four digit passcode 2009-01-12
From john:
i have a machine at home that has a four digit passcode and the numbers range from 1 to 4 how can i get all the ways those numbers can be used
Answered by Harley Weston.
The 2 rightmost digits 2008-12-18
From Peter:
Is there a pattern for the 2 rightmost digits of a power? For example, one problem for a math competition was what are the 2 rightmost digits of 3^1993?
Answered by Robert Dawson and Victoria West.
Student who is inverting digits 2008-12-09
From Tammie:
Do you have any strategies for addressing inversion of digits in two digit numbers. For example - The student the teacher is working with will write "14" and the number is 41. She has tried highlighting, practice writing numbers, and hundreds charts and finding patterns. Help! Thank you!
Answered by Robert Dawson and Victoria West.
I am a whole number less than 100 2008-12-03
From Cecelia:
If I am a whole number less than 100
and the sum of my digits is 4
and half of me is an odd number
What number am I?
Also am I prime or composite?

Answered by Penny.
A 4 digit number 2008-11-06
From Chris:
numbers 0 - 9 form a 4 digit number with no repetition.

It would round to 3000 if rounded to the nearest thousand

The digit in the tens place is twice the value of the digit in the thousands place.

It is an odd number.

It contains the largest digit.

It contains one digit less than 2.

The digit in the hundreds place is odd.

Can you find the 2 numbers?

Answered by Penny Nom.
4 digit combinations 2008-11-05
From Laura:
I need to know all the number combinations possible with a 4 digit combination with double zero in the middle???
Answered by Penny Nom.
What is the exact value of pi? 2008-09-27
From mahesh:
what is the exact value of pi.
22/7 is accurate value of pi, if not then how can i find out the exact pi value.

Answered by Harley Weston.
Repeating fractions 2008-09-09
From Juli:
My teacher recently put my math class to the test... We were deiscussing repeating fractions and she asked us to find out what the bar over a repeating decimal is called. I found out it was called the vinculum. But she also said to find out what the number under the vinculum was called. I can't seem to find it anywhere.
Answered by Penny Nom.
Hundreds, tens, and units digits 2008-09-05
From Cynthia:
write an expression for the value of a three-digit number whos hundreds, tens, and units digits are x, y, and z, respectively
Answered by Penny Nom.
3 digit combinatios from 0-9 2008-07-27
From Mike:
I need to know all the possible 3 digit combinations using the numbers 0-9. The numbers can be repeated as long as they are not of the same set. Example for not repeating: 123 is ok but not 321 or 231,132,213, etc. Please help me. Thanks, Mike.
Answered by Stephen La Rocque.
Sum of Digits 2008-07-24
From Warren:
If 100^25-25 is written in decimal notation, what is the sum of digits?
Answered by Penny Nom.
The number of digits in a really big exponent 2008-07-21
From Pete:
how would you find the number of digits in a really big exponent without a calculator?
Answered by Penny Nom.
The sum of the digits of two-digit number is 9 2008-07-01
From Audrey:
the sum of the digits of two-digit number is 9. if the digits are reversed, the new number if 63 greater than the original number. find the number.
Answered by Penny Nom.
A 7-digit odd number 2008-06-26
From Godryk:
I am the smallest 7-digit odd number. my ones digit is the sum of my thousands, and ten thousands digits. What number am I?
Answered by Penny Nom.
111...111 * 2003 2008-06-23
From Peggy:
Number a = 111...111 formed by 2003 1's. Find the sum of the digits of the number 2003 * a.
Answered by Penny Nom.
The sum of the digits of a number 2008-06-23
From Ben:
Question: Using mathematical induction, prove that if the sum of the digits of a number is divisible by three, then the number itself is also divisible by 3.
Answered by Penny Nom.
A 6 digit number 2008-04-23
From rajiv:
write the smallest 6-digit number using three different digits with 6 in the ten thousands place and 1 in the hundreds place
Answered by Penny Nom.
Rearrangements of the digits in 0123456789 2008-03-23
From Joe:
Found a close problem but not quite. Using digits 0123456789, how can I figure what all the different possibilities would be without repeating any digits? I know that there are 10! possible answers but how can I figure out what they are?
Answered by Stephen La Rocque.
A 4 digit passcode 2008-02-16
From Rob:
If there is a 4 digit passcode with only 6 punch in symbols, how many possibilities are there and what are they? symbols are: Y, X, RB, RT, LB, LT. Please get back to me, thanks for your time and help.
Answered by Stephen La Rocque.
Five digit combinations 2008-02-15
From Debbie:
I would like to get a list of all the possible 5 digit combinations of the numbers 12345.
Answered by Penny Nom.
A 2 digit number 2008-02-13
From Jenny:
The units digit of a certain two-digit number is one more than 4 times the tens digit. The number formed by interchanging the digits is 6 more than 3 times the original number. Find the original number.
Answered by Penny Nom.
7, 6, 5, 4, 3 and 2 digit numbers 2008-02-10
From Edward:
using the number 12345678 how many 7, 6,5,4,3 & 2 digit numbers can you make when not using any number twice in the same number
Answered by Penny Nom.
A positive integer with 2007 digits 2008-02-06
From Tom:
Prove that there's a unique positive integer of 2007 digits lenght, divisible by 2^2007, and made up solely by the digits 2 and 5.
Answered by Penny Nom.
A math riddle 2007-11-27
From Kathleen:
My 4th grade daughter was given a math riddle which she is expected to answer using a problem solving strategy. The question is:

The number of my hundreds and the number of my thousands is 3. The number of my tens is 7 times the number of my thousands. All my digits are different. What am I?

I have tried to come up with an answer, but am beginning to think it is less complicated than what I have come up with.

Answered by Stephen La Rocque.
Using the digits 1 to 9 2007-11-20
From sunjoo:
write the least whole number that uses the digits 1 though 9 once each. explain your answer.
Answered by Penny Nom.
A ten digit number 2007-11-11
From jeff:
find the greatest ten-digit positive multiple of 12 using each digit once and only once
Answered by Penny Nom.
The sum of the digits of a whole number is 200 2007-11-06
From Kristin:
If te sum of the digits of a whole number is 200, the whole number may not have ________ digits?
Answered by Penny Nom.
Show that there is no five-digit number which 2007-10-04
From Greg:
show that there is no five-digit number which uses each of the digits 1,2,3,4,5 such that the numbers formed by the first digit is divisible by 1, by the first two digits is divisible by 2 by the first three digits is divisible by 3, by the first four digits is divisible by 4, by the first five digits is divisible by 5
Answered by Stephen La Rocque, Claude Tradif and Victoria West.
Finding the last non-zero digits of large factorials 2007-10-04
From Mukesh:
i have to find last five non zero digits of integer which can be very large ( upto 10^12) . i can find last non zero digit of of any factorial. Now my problem is that i have to find last five non zero digit of factorial and also i want to general method for last K non zero digits of factorial n. For example 10!=3628800 so last non zero digit is 8 ,last two non zero digit is 88 .....and last five non zero digit is 36288.
Answered by Victoria West.
Three digit numbers where all digits are even 2007-09-14
From Cielo:
Hannah made a list of all of the three digit whole numbers where all three digit were even. How many three digit whole numbers were on Hannah's list?
Answered by Penny Nom.
A question about integers 2007-08-24
From Jerry:
Does there exist a positive integer such that when it is written in base 10 and its leftmost digit is crossed out, the new number is 56 times less than the original number?
Answered by Stephen La Rocque and Penny Nom.
who am i? 2007-08-08
From Phillip:
if you hold a mirror horizontally across my middle, i look the same in the mirror.if you hold a mirror between my second and third digits,i look the same in the mirror if you turn me upside down, i look the same. what 6 four-digit numbers could i be?
Answered by Penny Nom.
The smallest 5-digit even number 2007-06-26
From charles:
Using the digits 0,1,2,3,4 and 5 only once give the smallest 5-digit even number
Answered by Penny Nom.
All 4 digit combinations for numbers 0 through 9 2007-06-21
From Jessica:
How can I find all 4 digit combinations for numbers 0 through 9?
Answered by Penny Nom.
A 5 digit key 2007-05-31
From Michael:
I have a 5 digit key pad lock on my truck. I want to print out all of the combinations to try. pad one=0 pad two =1 pad three=2 pad four=3 pad five =4. can you help me find and print all combinations?
Answered by Harley Weston.
How many ways can I choose 4 numbers from 10? 2007-05-10
From Mitch:
Can you give me a list of all possible four digit combinations using 0 to 9 no repeat numbers and the numbers do not have to be entered in a special order. If you could also show me how to calulate this it would be great
Answered by Stephen La Rocque.
Seven digit account numbers 2007-03-09
From Miranda:
Account numbers for the Central Oil Company consist of seven digits. If the first digit cannot be 0, how many account numbers are possible? Thank you so much!!!
Answered by Penny Nom.
Four digit numbers 2007-02-26
From Anton:
Hello! I would like to ask you how many combinations are possible using 4 digit number. # # # # (1...9).There is no zero,numbers don't repeat,second and forth are odd.Thanks
Answered by Penny Nom.
A two-digit number is five times its units digit. 2007-02-21
From Pamela:
A two-digit number is five times its units digit. If the digits are reversed, the resulting number is 27 more than the original number. Find the original number.
Answered by Gabriel Potter and Penny Nom.
*** x ** = **** 2007-02-16
From Dani:
Use the numbers 1-9 only once to make the following: A three digit number times a two digit number that gives a four digit number. That is *** x ** = **** (the numbers 1-9 can only be used once for each star). I came up with the answer 138 x 42 = 5796 but I want to know whether this is the only solution and if not, is there a formula to come up with the answer. Thanks! I appreciate your help!
Answered by Chris Fisher and Claude Tardif.
The sum of the digits of a two-digit number is 13. 2007-01-27
From Liz:
The sum of the digits of a two-digit number is 13. If the digits are reversed, the new number is 9 more than the original number. Find the original number.
Answered by Penny Nom.
2 digit combinations 2006-12-04
From Gary:
please figure out for me what are the 2 digit combinations of numbers using numbers 0 thru 9
Answered by Penny Nom.
My greatest digit is 9, ... 2006-11-17
From Tiffany:
My greatest digit is a 9, but less than 900. I'm one more than a multiple of 10 and the sum of my digits is 12. Who am I?
Answered by Penny Nom.
How can half of 12 be 7? 2006-11-16
From Liz:
How can half of 12 be 7?
Answered by Steve La Rocque, Chris Fisher and Penny Nom.
What is the highest number possible with 3 digits? 2006-11-16
From Liz:
What is the highest number possible with 3 digits? The teacher said the answer is not 999 and that the question did not say "3-digit number." My answer then is 9 to the 99th power (written mathematically of course) as this uses "3 digits" and is obviously a huge number. Is this correct?
Answered by Stephen La Rocque.
Four digit combinations 2006-10-26
From Sasha:
CAN YOU LIST ALL OF THE POSSIBLE 4 DIGIT COMBINATION'S, THAT DO NOT START WITH 0?
Answered by Stephen La Rocque.
Write the digits 1 to 9 on index cards, ... 2006-10-19
From Kim:
Write the digits 1 to 9 on index cards, arrange the cards to form three 3-digit numbers (using each card only ONCE). The third number is the sum of the first two numbers ** how many different ways can you do this?? **
Answered by Penny Nom.
What number could it be? 2006-09-27
From Jonathan:
What number could it be?

It is between 12000 and 13000
Its hundreds, ten and ones digits are all odd
the sum of all its digits is 12.

Answered by Steve La Rocque and Claude Tardif.
A three-digit number multiplied by 7, then 11, then 13 2006-09-17
From Sherrie:
why is it true that a three-digit number multiplied by 7, then 11, then 13 will result in the three digits repeated twice?
Answered by Stephen La Rocque.
How many different three-digit numbers can you make using ... 2006-09-12
From Beth:
How many different three-digit numbers can you make using the numbers 2, 5, 7, 8 using the digits any number of times?
Answered by Stephen La Rocque and Penny Nom.
Two characters 2006-09-12
From Robert:
I am looking to find out how many possible unique combinations I can have if at any time i can use only two characters of numbers or the alphabet...For ex., i can have 1-99 or i can have a1, a2, z1, z2 ... or i can have aa, ab, ac... i came up with possible combinations of 1295 or so... can you help?
Answered by Penny.
The last two digits 2006-07-22
From Sam:
You have answered this question already but you only answered to one digit.

What are the last TWO digits of:
3 to the power of 1994
7 to the power of 1994
3 to the power of 1994 + 7 to the power of 1994
7 to the power of 1994 - 3 to the power of 1994


Answered by Paul Betts and Penny Nom.
The last digit of a six-digit number is 2. 2006-07-09
From GG:
The last digit of a six-digit number is 2. If the 2 is moved to the start of the number, the new six-digit number is only a third of the original number. Find the original number.
Answered by Paul Betts, Chris Fisher, Penny Nom.
How many digits are in the number 2^64? 2006-06-14
From Trang:
How many digits are in the number 264?
Answered by Stephen La Rocque.
We are 2 pairs of consecutive 2 digit numbers ... 2006-05-13
From A perent:
We are 2 pairs of consecutive 2 digit numbers that are factors of the number of feet in a mile. Who are we?
Answered by Claude Tardif.
10^100 in binary form 2006-05-10
From Headmaster:
How many digits has the number 10100 if we write it in binary form?
Answered by Chris Fisher, Paul Betts and Steve La Rocque.
8-digits numbers with their digits in decreasing order 2006-05-09
From Headmaster:
How many 8-digits number are there with their digits in decreasing order
Answered by Penny Nom.
A number theory problem 2006-05-05
From DeHayward:
Find the 6-digit number in which the first digit is one less than the second, the third is half of the second, the fourth is 3 times the third, and the last 2 digits are the sum of the fourth and fifth. The sum of all the digits is 24.
Answered by Paul Betts.
The sum of a three digit number and its three individual digits is 429 2006-04-08
From Megan:
Gill has recently moved to a new house, which has a three- digit number. the sum of this number and its three individual digits is 429. What is the product of the three digits which make up the house number?
Answered by Chris Fisher.
Four digit numbers 2006-03-25
From Kenvin:
i was wondering how many possibilities is there for a four digit number with the same first two numbers and the last two is not one of the first with numbers 1-9
Answered by Stephen La Rocque.
Five digit numbers 2006-03-25
From Tony:
Can someone tell me how many unique five digit numbers can be generated using 0-9?
Answered by Stephen La Rocque and Penny Nom.
The first six million digits of PI 2006-03-08
From Lori:
How many threes are there in the first six million digits of PI? Also how many nines?
Answered by Stephen La Rocque.
A nine digit number 2006-03-06
From Ryan:
What is the total number of possible combinations of a nine digit number (ie., social security number) including repeating numbers?
Answered by Stephen La Rocque and Penny Nom.
Counting digits 2006-01-30
From Cynthia:
I would like to know the easiest way to calculate the total numbers of digits used by a printer to number the pages of a book from 1 to 250.
Answered by Penny Nom.
The number of combinations of the digits 0235588 2005-12-07
From Blake:
If you have the digits 0235588 how many different combinations can you possibly form with these seven digits?
Answered by Penny.
Fill in the blanks 2005-12-05
From Bonnie:
Distribute the numbers 1 through 9 on the lines below so that two equations are true.

_ _ x _ = _ _

_ x _ = _ _

Use each digit only once-

Answered by Penny Nom.
Add one 1 at the beginning and at the end of a number 2005-11-13
From Samuel:
If we add one 1 at the beginning and at the end of a number, this number is increased by 14789. What is the sum of the digits of the number?
Answered by Penny Nom.
5 digit numbers that include 5 and exclude 8 2005-11-04
From Paul:
figure out how many 5 digit numbers are there that include the digit 5 and exclude the digit 8. show me how to do get to the answer. (23816)
Answered by Paul Betts.
Four digit numbers 2005-10-09
From David:
I had a discussion with my father about how many four digit numbers you can make with 0-9. He was saying that there is 12,000 and that seems quite high for me. But can you tell me how many there are, and what exactly are they?
Answered by Penny Nom.
Three digit numbers 2005-10-04
From Jordan:
i need to know how many 3 digit numbers there are
Answered by Penny Nom.
What is my number? 2005-09-16
From Bob:
I have 6 digits. 100,000th digit is one less than my ones digit, eight greater than my 1,000's digit, twice my tens digit and four times my 100s digit. My 10,000s digit is 0 What is my number?
Answered by Penny Nom.
What is the ones digit of 3 to the 79 power? 2005-09-14
From Candice:
What is the ones digit of 3 to the 79 power?
Answered by Penny Nom.
Whats the value of the digit 7 in 756,809? 2005-09-14
From Anastasia:
Whats the value of the digit 7 in 756,809?
Answered by Penny Nom.
The number of four digit combinations 2005-08-09
From Kevin:
My 12 year old has asked me how to figure out the number of four digit combinations possible using 0 thru 9 without repeating a number?
Answered by Penny.
A two digit number 2005-08-09
From Grace:
I am a 2 digit number. Both of my digits are even. My tens digit is 8 more than my ones digit. What number am I?
Answered by Penny Nom.
The sum of the digits of 2^100 2005-06-11
From Richard:
The sum of the digits was calculated for the number 2100, then the sum of the digits was calculated for the resulting number and so on, until a single digit is left.
Answered by Penny Nom.
How many digits? 2005-06-07
From Floren:
The numbers 21989 and 51989 are written one after another. How many digits in all are there?
Answered by Claude Tardif.
A six digit answer 2005-05-18
From Angela:
I have a 6 digit answer that is comprised of only 4 symbols: a square, a circle, a triangle, and an X. How many possible solutions are there and how is the best way to find out what ALL the solutions are?
Answered by Penny Nom.
Some four digit numbers 2005-04-16
From Lori:
can u give me every possible combination of four numbers starting with the number three
Answered by Penny Nom.
The sum of the digits 2005-03-16
From kelsey:
What is the sum of the digits in the decimal form of 21999 * 52002?
Answered by Claude Tardif.
How many three digit numbers can I make from the four cards 2005-03-12
From Sue:
I have four playing cards 2,3,4,5 of hearts. How many three digit numbers can I make from the four cards.
Answered by Penny Nom.
Six digit numbers with at least one 7 2004-12-27
From Behzad:
How many six-digit numbers contain at least one 7 in their decimal expansion?
Answered by Penny Nom.
Strings of 4 digits from 1,2,...,7 2004-12-09
From Tom:
How many different combinations can be made of the numbers 1-7 in 4 string combinations in any order? EX:7-2-3-5, 3-5-1-7, etc...
And if you were to include the same 2 numbers in every combination, how many would that make? EX: Using 1 & 2: 1-2-7-4, 5-1-4-2, 2-7-5-1, etc...

Answered by Penny Nom.
A five digit number 2004-10-06
From A parent:
What is the 5 digit number in which the first 2 digits are the square of the 3rd digit and the last 2 digits are the square of the digit that is one less than the third digit? The sum of all the digits is 22.
Answered by Penny Nom.
A palindrome question 2004-09-28
From Lilly:
12, 21, 13, and 31 are the only double-digit numbers whose squares are the palindromes of the squares of the palindromes of double-digit numbers. I was wondering why it works for these numbers, and if only these numbers work this way.
Answered by Chris Fisher and Penny Nom.
Four and five digit numbers 2004-09-21
From Josy:
The question I have now in front of me is....Is a 4-digit number always less than a 5-digit number? Hi Josy, The digits in order are 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9. Thus the largest four digit number is 9999. The smallet 5 digit number is 10000. Penny Go to Math Central
Answered by Penny Nom.
Some numbers less than 100 2004-09-17
From Paul:
for how many numbers less than 100 is the digit in the ones place half the digit in the tens place?
Answered by Penny Nom.
The bar over repeating digits. 2004-09-07
From Debbie:
I would like to know the name given to the bar that is written over the repeating digits of a decimal.
Answered by Penny Nom.
Four digits 2004-07-10
From Rob:
I am always interested to know how the for digit works. I mean, you have correctly put it that the total numbers obtain from 0000 thru 9999 are 10,000. My question is, is there any simple formula to turn this simple 4 figures of say: 1234.
Answered by Penny Nom.
Jack's social security number 2004-06-08
From A student:
Jack's social security number contains each of the nonzero digits exactly once. By examining the digits from left to right, he also found that 1 divides the first digit evenly, 2 divides the sum of the first two digirs evenly, 3 divides the sum of the first three digits evenly, and so on, until 9 divides the sum of all the digits evenly. What is Jack's social security number?
Answered by Penny Nom.
A 3 digit number divisible by 7 2004-05-03
From A student:
We need to arrange 1,3 and 6 to form a 3 digit number that is divisible by 7.
Answered by Penny Nom.
Digits in the decimal expansion 2004-02-11
From Leslie:
In the decimal expansion of 1/17 what digit is in the 1997th place?
Answered by Penny Nom.
The digits in 349 2003-09-12
From Franik:
in the number 349, which number has the least value, and why?
Answered by Penny Nom.
7,473,000,000 divided by 52000 2003-09-06
From A student:
I am having trouble with a question. 7,473,000,000 divided by 52000. Our calculater gets 147311.5385. I come up with 143711.53846, and then the number starts to repeat itself
Answered by Penny Nom.
Four digit combinations 2003-09-04
From Emma:
I seriously need to find out all the four digit combinations from 0 to 9!!! My name Is Emma Dibitt and I'm going into 8th grade and I'm a student!!!
Answered by Penny Nom.
The units digit of 57 to the 28th power 2003-09-01
From Maria:

If 57 is raised to the 28th power, what must be the units digit in the result?

If you raise 7 to the 500th power, what is the numeral that will appear in the units digit position?


Answered by Penny Nom.
39 consecutive natural numbers 2003-08-19
From A student:
Prove that among any 39 consecutive natural numbers it is always possible to find one whose sum of digits is divisible by 11.
Answered by Penny Nom.
Inserting a comma ever three digits 2003-07-25
From Linda:
when writing a large number, why do we insert a comma every three numbers instead of every two or four numbers?
Answered by Penny Nom.
Four digit palindromes 2003-05-05
From Heather:
How many palindromes were in between the numbers 1000 and 9999?
Answered by Penny Nom.
Three digit number 2003-03-10
From Grace:
What three digit positive integer is exactly 32 times the sum of its digits?
Answered by Claude Tardif.
Combinations of 1,2,3,4,5 and 6 2003-02-01
From Kyle:
Today I was aked a question by my geometry teacher. It was, what is the sum of all the possible combinations of the numbers 1, 2, 3, 4, 5, and 6. He said all the possible combinations were 720. I would like to know how u could do this, and what the answer is.
Answered by Penny Nom.
6 digit numbers from 0,0,2,2,4,4 2003-01-23
From Amanda:
How many 6 digit numbers can you make from the numbers 0,0,2,2,4,4, giving that 0 cannot come first. The number has to contain 2 twos, 2 fours, and 2 zeros.
Answered by Penny Nom and Claude Tardif.
4 x abcd = dcba 2002-11-20
From A student:
Say you have a four digit number (e.g. abcd) and you multiply the number by 4. The answer you get will be the reverse order of the number you started with (dcba). What is the number? The four digits (a,b,c,d) cannot be the same number or cannot be repeated.
Answered by Penny Nom and Claude Tardif.
Rounding 27.27 2002-11-03
From A parent:
If you have a problem 27.27 and you need to round to the first 7 the answer would be 27

Would 27.0 be acceptable as well or is it completely wrong.


Answered by Penny Nom.
What are the digits? 2002-10-24
From Ebenezer:
There are three digits. The middle digit is zero and the sum of the first and last digits are is 13. When the number is reversed it is increased by 297. What are the digits?
Answered by Penny Nom.
Use each digit 1-9 only one time each,... 2002-10-19
From Megan:
Use each digit 1-9 only one time each, divide the numbers into 3 groups, make one 2 digit number, one 3 digit number, and one 4 digit number. There are 6 combinations of these numbers in which you can multiply the 2 digit and 3 digit number together to get the 4 digit number (using each digit 1-9 one time each). What are they!!!!!!!!!????????????
Answered by Claude Tardif.
I am a 3 digit number. 2002-09-06
From Jasmine:
I am a 3 digit number. My last digit is 3 times my first digit. My firat digit is twice my middle digit. What numbers am I? There are at least 2 correct answers?
Answered by Paul Betts.
Counting 2002-06-21
From Rachel:
How many different numbers of 2 different digits each can be formed using the digits (1,3,5,7,9)?

How many triangles are formed by the vertical of a regular hexagon?

Answered by Penny Nom.
Numbering pages 2001-11-15
From Lucy:
A printer uses 1008 digits to number the pages of a book. How many pages are there in the book?
Answered by Penny Nom.
The 100 chart 2001-09-28
From Nich:
Am I suppose to use the 100 chart for these questions.

Question One:
I am a 2 digit number my tens digit is 2 more than my one digit my 1 digit is between 4 & 6. What # am I ?

Question Two:
I am a 2 digit # I am greater than 40 but less than 60 my tens and ones digits are the same I am a odd number what am I ?


Answered by Penny Nom.
I have 6 digits. 2001-09-06
From Kristan:
I have 6 digits. My hundred thousands is 1 less than my 1 digit, 8 greater than my thousands digit, twice my tens digit, and 4 times my hundreds digit. My ten thousands digit is 0. What # am I?
Answered by Penny Nom.
How many 6 digit numeral combinations 2001-04-26
From Bryan:
How many 6 digit numeral combinations are there If you can only use 6 digits (1, 2, 3, 4, 5, 6) and no number can be used twice in the Numeral!
Answered by Claude Tardif.
The number of occurrences of 0 is __, of 1 is __, of... 2001-04-17
From Martyanne:
"In this sentence the number of occurrences of 0 is __, of 1 is __, of 2 is __, of 3 is __, of 4 is __, of 5 is __, of 6 is __, if 7 is __, of 8 is __, of 9 is __."

Each blank is to be filled with a numeral of one or more digits, written in decimal notation.

Answered by Claude Tardif.
The repetend in repeating decimals 2001-03-21
From Sharon:
What is the name for the bar over the repetend in repeating decimals? Also, what is the name of the long division "house"?
Answered by Penny Nom.
The sum of all ten-digit numbers. 2001-01-10
From John:
Compute the sum of all ten-digit numbers. Can you determine the sum of all n -digit numbers?
Answered by Sukanta Pati.
Divisibility by 16 2000-12-12
From Shiling:
A number can be divided by 16 if and only if its 1st four digits can be divided by 16. How can you prove that?
Answered by Penny Nom.
Six digit numbers using 1,2,5,6,7, and 9 2000-03-20
From Rachel:
How many different six-digit numbers can you make using the digits 1,2,5,6,7, and 9? How many of these six digit numbers are divisible by six?
Answered by Claude Tardif and Denis Hanson.
Bases other than 10 1999-12-06
From Garret Magin:
We are doing a lesson on numbers of other bases than 10. We are working with binary, octal, and Hexadecimal. I was wondering what is used to represent number of different bases other then 16? Does it just continue on with the alphabet and if so what happens when you get to Z. It would be a help if you could answer this because it is really bugging me. And none of the math teachers at my school could let me know.
Answered by Claude Tardif and Patrick Maidorn.
Numbers with the digit 2 in 1...1000 1999-09-20
From Jessica:
Is there a trick to finding out how many numbers containing the digit two is there from 1 to 1000?
Answered by Walter Whiteley.
A Puzzle 1998-10-27
From Bruce Bragnu:
We are trying to solve what SHOULD BE a simple 7th grade problem and have run into a wall.
It is:
ABCD
ABCD
ABCD
ABCD
-------
EBEA

It is an addition problem. Each particular letter represents the same digit. We are looking for what number "B" represents. We have tried a multitude of solutions and have come up empty.
Answered by Penny Nom.

Social Security Numbers 1998-07-07
From Valerie Lucas:
How many social security numbers are possible?

the answer is 10^9

why isn't the answer 9^9?
Answered by Harley Weston.

The two-digit numbers from 10-99 1998-01-21
From Alexis Riddle:
My name is Alexis. I'm a student in 8th grade and I'm taking Algebra I Honors. My question is: In a string of numbers, two adjacent digits are considered as a two-digit number. For instance, the string 11012 contains the numbers 10, 11, and 12. What is the number of digits in the smallest string that contains all of the two-digit numbers from 10-99? Please help and thank you for any assistance you can give me.
Answered by Penny Nom.
Driving me CRAZY. 1997-11-17
From Billy Tran:
Write a two digit number (both digits different and neither equal to zero) and then express the same number but now composed of the same two digits in reverse order with some mathematical symbol (+, -, *, /, roots, !, or exponents). for example: 25 = 5^2. Now give me another.

Hope you get this, cause its driving me CRAZY
Answered by Penny Nom.

How many digits are there in 2^2520? 1996-10-07
From Rita Leung:
A)The number 64 is a sq., a cube, and a sixth power because 64=8*8, 4*4*4, 2*2*2*2*2*2. Find the smallest integer greater than 1 that is a sq., a cube, a 4th, 5th, 6th, 7th, 8th, 9th and 10th power. I have found that the answer is 2 to the power 2520th.
B) How many digits are in the correct answer to part A? The answer is uncertain. It is either 758 or 759. Can you give me any ideas?

Answered by Penny Nom.
Repeating decimals 1996-09-09
From Alice:
What is the line called that is placed over the decimal to show that it is infinitely repeating?
Answered by The Centralizer.
 
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