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A combination lock 2019-08-01
From markbo:
A combination lock has 0-9 plus Y on its keypad. A code is generated by selecting 4 digits from those keys (0-9 and Y) with no repeated choices, but sequence does not matter
(i.e. 1-2-3-4 is the same as 4-3-2-1, and the same as 3-4-1-2 and counts as one combination)

How many different 4-digit codes are possible in this scenario?

Answered by Penny Nom.
Combination lock 2019-07-31
From Antony:
So my 3yr old daughter has had a bit of a play with the 3 dial combination lock on my backpack and locked it closed.
I am looking for all the possible combinations to go through a process of elimination to find the combination she has set.
To be clear. There are three dials, each with the numbers 0-9. I have read 10x10x10=1000 options but not sure if that is correct .. feels too small?
Many thanks in advance.

Answered by Penny Nom.
An inline lock with four rows 2019-06-05
From Edward:
I have a inline lock with four rows of numbers 0-9.The numbers cannot be repeated. Can you please print the possible codes so I can go through them one at a time. The lock and the cable cost $300. Don't want to pitch it. You guys are lifesavers, can't wait to hear back. Thanks.
Answered by Penny Nom.
A 4 digit combination lock 2019-02-02
From Brijanshu:
I have a lock that contain only four no. 6,7,8 & 9 . How many possible password of four digit containing these Number.
Answered by Penny Nom.
When are the hands of a clock perpendicular? 2018-01-11
From Nazrul:
How many times in a day are the hands of a clock perpendicular to each other? How can I find the times? Please help me.
Answered by Penny Nom.
A lock with 3 tumblers 2017-07-29
From Carol:
I have a lock that has 3 tumblers. The numbers are 0 - 9. I cannot recall what I set the combination to. How many combinations will there be with three numbers?
Answered by Penny Nom.
Filling cinder blocks with concrete 2017-04-24
From Katherine:
I am looking to construct a 10 X 10 dance floor using 8 x 16 cinder blocks.

I have figured that I will need about 120 blocks, however I am not sure how much concrete I will need to fill the total empty space.

Thank you

Answered by Penny Nom.
A block base for a plywood rectangle 2017-02-18
From Joe:
How many cinder blocks 16x8 would i need to build a solid base for a plywood base 54inches wide and 30 inches deep Thank you
Answered by Penny Nom.
The area of a city block 2016-12-08
From Miura:
A city block is three times as long as long as it is wide.if the distance around the block is 0.48 kilometers, what is the area of the block in square meters?
Answered by Penny Nom.
A key for a lock with five tumblers 2016-11-02
From Aeriel:
A lock works by having a key turn a sequence of tumblers. Consecutive tumblers have different heights, and in order to unlock the lock, the sequence of heights on the key must exactly match those of the lock. The picture below shows a lock with four tumblers. How many different keys can be made for a lock that has 7 tumblers with 5 possible heights each?
Answered by Penny Nom.
A block wall 2016-03-15
From Robert:
I have a wall 40 ft. long and 4 ft. tall as well as another one that is 30 ft by 3.5 ft. tall that I am trying to build. how many 6 inch by 12 inch landscaping blocks do I need?
Answered by Penny Nom.
Compressed Earth blocks 2016-03-02
From John:
how many 14"x10"x4" blocks do I need for a 1300sq foot house 8 foot high
Answered by Penny Nom.
The combination to a locker 2015-11-11
From Jason:
I can't seem to open my locker cause I forgot the combination, the numbers are 1-8 Without repeat for 4 number for example 1234 or 2345 for numbers 1-8 without any repeat.

Answered by Harley Weston.
The weight of a steel block 2015-04-04
From Mark:
the weight of a steel cube 37 inches X 28 inches X 7 inches
Answered by Penny Nom.
A lost combination 2014-09-28
From Kim:
I cannot remember my combo to this simple lockbox. It is 3 digits- from 0-9. They can be used more than once . I thought it was 117..but no joy. I am fairly sure it was using those digits 1, and 7. can you give me a list of all possible combinations, using 1s and 7s, for the 3 number code? Thank you and I am in awe of people who have math skills, for I certainly do not.
Answered by Penny Nom.
Three digit padlock combinations 2014-03-20
From Edwin:
Would appreciate if you can provide me with the list of different combinations that can be obtained from a three digits number. I lost the access code of a three digits number padlock (and need to open it order to get important documents
Answered by Penny Nom.
An extension using concrete blocks 2013-10-30
From david:
hi how many concrete blocks would i need for an extension 50 ft long ,20 ft wide and 12ft height
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.
A clock takes 3 seconds to strick the hour of 3 o'clock 2012-03-09
From saptarshi:
[ A clock takes 3 seconds to strick the hour of 3 o'clock. How many seconds will it take to strick 9 o'clock?]
Answered by Robert Dawson.
A lost combination 2012-03-06
From pam:
I lost the combination for my luggage that I haven't used for many years. It is a 3 digit combination. I'm pretty sure only these numbers could have been used: 0,1,2,3,7,8,9. Can you give me a calculated list of all these combinations?
Answered by Penny Nom.
Tiling a floor 2012-02-27
From jamie:
how many 16in by 16in blocks would it take to cover a 16ft by 16ft floor?
Answered by Penny Nom.
Blocks in a wall 2011-09-12
From JOHN:
Answered by Harley Weston.
A lock box 2011-08-03
From Tom:
I need to open a lock box from my parent's estate. The combination is a simple 4 number lock. The last two numbers are 33. Numbers can be used more than once.What are the possible combinations? WP
Answered by Harley Weston.
A punch-code lock box 2010-11-29
From Doug:
I am a real estate agent that uses punch-code lock boxes on houses to store the keys. I need to crack the code on one of our boxes, so I need a list of the possible combinations.
4 digit code
Numbers 0-9
Each number can only be used once
Order of the numbers does not matter.

With advice from this site, I have calculated that there should be 210 possibilities. 10x9x8x7 (5040) gives me the total number possibilities and 4x3x2x1 (24) gives me the total number of ways to arrange those numbers. So if I divide the possibilities by the arrangement, I get 210. (5040 / 24 = 210) GREAT!!!

Now, how do I develop a list of those 210 combinations?

Thanks for your help.

Answered by Robert Dawson.
The equation of a circle 2010-10-20
From Silvan:
Hi, I just want to find the x,y values for the circumference of a circle...

Lets take a clock having its centre at (0,0) in a graph. I just want to know how to find the (x,y) co-ordinates for the curved path or the surface of the circle.. Is there any formula to directly align the curved path or the circumference of the circle in a graph for a known radius of a circle..

I feel it will be useful for me to draw a clock in a graph... :-)

Answered by Penny Nom.
The distance travelled by a minute hand 2010-03-06
From Patric:
How much distance will the minutes hand of length 14mm of a clock cover in moving from 5 to 10?
Answered by Penny Nom.
A push-button padlock 2010-01-17
From Vince:

I have a push-button padlock using ten buttons (1-2-3-4-5-6-7-8-9-0). Five digits must be pushed in order to open the lock. Each digit can only be used once. Order is not supposed to matter.

How many different possible combinations? And what are they?

Answered by Harley Weston.
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.
Number of Concrete Blocks 2009-08-06
From Simone:
Hi there, I have a quote to complete and I need to figure out the formula that will tell me how many concrete blocks I need to cover a certain area. Blocks can either be 8in or 12in. The area that I am looking to cover with blocks is 30182 sq ft. Thank you for your assistance.
Answered by Janice Cotcher and Stephen La Rocque.
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.
My son has locked his ipod and can't remember the combo. 2009-03-27
From peggy:
my son has locked his ipod and can't remember the combo. He knows it has the numbers 2-5-8 in it but not the fourth number or the order. could you help us?
Answered by Robert Dawson.
I lost the combo to my lock box 2009-01-10
From Rob:
I lost the combo to my lock box, I remember 2 of the #'s in the combo are 6, but dont remember which ones. What are the possible scenarios knowing the above? Thanks!
Answered by Stephen La Rocque.
Percentage of an hour 2008-10-15


Answered by Penny Nom.
A three 0-9 tumbler lock 2008-09-22
From Louis:
I recently gave my daughter an old briefcase which uses a three 0-9 tumbler lock. She set the lock and now she canít open one side. Q. Is there a 3 digit combination number generator available to give me the 1000 possibilities?



PS In this type of lock you can repeat the same digit three times.

Answered by Penny Nom.
How many city blocks in a mile? 2008-08-14
Answered by Penny Nom.
Concrete blocks 2008-06-18
From marvin:
How many cement blocks do i need to build a 8 ft. tall wall x 1,300 ft. long?
Answered by Harley Weston.
The angle between the hands on a clock 2008-04-04
From Kristin:
The question I need help with is : Bobo looked at the clock at 1:25. What was the precise measure of the angle formed by the hour and minute hands of the clock? Assume that each of the clock hands moves at a constant rate continuously around the face of the clock. Thus, in any given fractional part of an hour, each hand will move that same fractional part of an hour's worth of movement.
Answered by Stephen La Rocque.
A briefcase lock 2008-02-11
From Alfred:
A briefcase lock has 3 columns of numbers each 0-9. It opens with the correct combination of three numbers. How many combinations are possible to open the lock.
Answered by Penny Nom.
A 24 hour clock 2008-01-31
at a certain time i looked at a 24-hour digital clock and noticed some things about the time. (1 The number in the hours section plus the number in the minutes section makes 60.(2 One of the digits in the minutes section is the square root of the other digit in the minutes section.(3 The sum of the digits in the minutes section is the number in the hours section reversed. what is the time?
Answered by Penny Nom.
A 5 button lock 2008-01-02
From mandy:
i have a problem. I have a 5 button lock.and i seem to have forgotten the combination. You can only push each button once but you can push more than one button at a time and you don't have to use each button but i am pretty sure i used all five. for example it can be 1,2,3,4,5 or 1,2&3,4,5. I was wondering if anyone can get me a list of all the possibilities because i really need to get the box open.
Answered by Penny Nom.
Partitioning a clock face 2007-12-19
From Kim:
Using a clock with a regular circular faced dial, draw two straight lines such that the sum of the numbers in each of the three areas is equal.
Answered by The team at Math Central.
A 3 digit lock 2007-11-06
From Michael:
We have a 3 digit lock that only allows for 5 possible numbers to be used. (The numbers can repeat) What are the total number of combinations that can be created.
Answered by Penny Nom.
The digital lock for a cell phone 2007-08-29
From Hollie:
i have a four digit lock code on my cell phone and cannot remember what it is. i know that it does not contain a 2 or a 4 and none of the numbers are repeated. the numbers range from 0 to nine and the only way to figure out what the code is, is to try randomly. I was wondering if you could give me a list of possible combinations using the information i gave you to make it easier to crack the code.
Answered by Penny Nom.
An old bike lock 2007-08-08
From Jeremy:
I have an old bike lock i found in the garage of the house i just moved in to. It has four columns and the nubers are 1 through 6. I understand that there are 1236 (6x6x6x6) possibilities. Is there a graph of all the possible combinations cuz i looked all over the web and couldn't find one.
Answered by Penny Nom.
Five button push lock 2007-07-06
From Jeffrey:
We have a 5 button push lock and we were wondering how many different codes were possible in this situation. In this lock each button can only be pressed once (ie it's not a numbered key pad) and order matters. How would we find out the # of possible codes?
Answered by Stephen La Rocque.
The combintion of a bike lock 2007-07-01
From Tricia:
I have a bike lock that I know the numbers 3, 6, 8, & 9 are part of the combination, but I can't remember the order. What is the calculation to get all of the possible combinations.
Answered by Stephen La Rocque.
The lock code for my phone 2007-06-30
From Amanda:
okay so i forgot my lock code for my phone its four digits but i know it doesn't have a 1 or a 0 in it so it has to be from numbers 2 to 9 i need to know all the four digit combinations asap cause i cant use my phone till can someone please help me Amanda
Answered by Penny Nom.
Rate of change of distance between the clock hands 2007-06-05
From Jonathan:
A certain Clock has a minute hand with a length of 4 inches long and an hour hand with a length of 3 inches long. How fast is the distance between tips of these hands changing at 9:00?
Answered by Stephen La Rocque.
A push button lock 2007-05-21
From Werner:
I have a push button lock (the numbers entered does not have a start and end i.e. 1234 = 4321 or 2341 = 3241 ...)

So if it is a 4 digit code and you have 10 buttons (0 to 9) there should be 5040 (?) possibilities and how would I list these unique combinations

Answered by Penny Nom.
4 digit lock 2007-05-16
From Kathy:
Hi, My name is Kathy and I'm a REALTOR, I have 2 different lockboxes that I cannot remember the combinations for, so what I need is all the different combinations for 4 digits that cannot be the same, i.e. 0123. Can you help me out? I would hate to throw them away as they cost about $30 each. Thank you, Kathy
Answered by Stephen La Rocque.
Understanding fractions and their equivalents 2007-04-02
From Gail:
How can I get fourth grade students to understand fractions and their equivalents?
Answered by Diane Hanson.
Angle of clock hands 2007-01-31
From Sophia:
How many degrees are in the aute angle formed by the hands of a clock at 2:20 p.m.?
Answered by Stephen La Rocque.
Bike combination lock 2006-07-16
From Alejandra:
I have a bike lock. It has three columns of the digets 1-9 and zero. I have forgotten the combination. Three numbers need to be imputed. What are the possible lock cominations, so that i can try to break the lock?
Answered by Stephen La Rocque.
A 5 digit, push-button door 2006-06-20
From George:
We have a 5 digit, push-button door look (1-5). How many combinations are possible without repeating a number in a 3 digit entry code?
Answered by Stephen La Rocque.
A 4-digit Combination Lock 2006-03-09
From Adam:
I have a 4-digit Combination Lock but i have forgotten the code. i do know that it is an even number, all the digits are different, the second digit is zero and the largest digit is 6. what are all the possibilities.
Answered by Stephen La Rocque.
A 3 by 3 block on a calendar 2006-01-18
From A student:
Choose two different blocks of nine numbers arranged 3 across and 3 down on a calendar, and check that this rule holds: For any block of nine numbers the average of the four corner numbers is equal to the middle number. Show your work and explain why the rule works.
Answered by Penny Nom.
Blocks in a mile in Phoenix Arizona 2005-11-30
From Rita:
How many blocks are there in a mile in our city of Phoenix, Az.?
Answered by Penny Nom.
A combination lock 2005-10-03
From A bicycle owner:
What are the number of permutations (Combinations?) of a combination lock of a cylinder with four separate movable rings. Each ring has the numbers from one to six (six "permutations" per ring).

This is a bicycle lock.

I was told that it is 62 (6x6x6x6) = 1296.

Is this correct?.

Answered by Penny Nom.
A combination lock has 60 positions... 2005-02-07
From Kathy:
A combination lock has 60 positions arranged in a circle to which a pointer may be set. Three settings are required to open it and no one setting may be closer than 5 positions from the immediately preceding setting. How many different locks may be manufactured?
Answered by Penny Nom.
A 4-digit access code 2005-01-02
From Missi:
I need to find the 4 digit number to access my voice mail. These numbers will be 0-9 & numbers can be repeated. Could you provide me with a list of possibly combinations? If not, do you know anywhere that I could get a list of combinations so I don't have to write it all down?
Answered by Harley Weston.
Safe cracker 2004-09-09
From Adam:

Franklin's friend had taken an item from him, and put it in his family's safe, when franklin went to retrieve it he came to a combination lock on the safe, with the dial numbers going from 0 to 59. Unfortunately, he wasn't sure whether there were three or four numbers in the combination, or even which direction to turn the wheel

If it takes him 15 seconds to try a single combination, how many days will it take him to to try every possible combination? Please round to the nearest day.
Answered by Penny Nom.

The number of blocks in a mile 2004-07-18
From Valerie:
I don't know if you can help me but I was wondering how many blocks are in a mile in Ocean City, New Jersey?
Answered by Penny Nom.
The combinatiion for a keybox 2004-05-17
From Darrin:
I have a puzzle question based on reality. I have a real-estate type keybox (Supra) that has 10 digits, 0-9. I am trying to figure out a methodical way to test all number combinations to it to open it. (totally legal- it was taken from the trash at a jobsite since they couldn't open it!) The combination could be any or all of the digits, but any digit is only used once. This is not like a simplex lock problem where a combination of keypresses would be different- i.e. 1,2,3 is the same as 1+2,3. Any ideas?
Answered by Penny Nom.
Why the word combinations? 2004-05-05
From Megan:
Why are locker combinations called locker combinations not locker permutations. The order of the numbers matter so why aren't they called locker permutations.
Answered by Claude Tardif and Penny Nom.
A clock chimes 7 times in 7seconds 2004-05-02
From Anna:
A clock chimes 7 times in 7seconds. how long does it take the clock to chime 10 times?
Answered by Penny Nom.
Transformations of pattern blocks 2003-02-06
From Cheryl:
I am trying to help my 8th grade son with Transformations - use of patttern blocks. He has to trace a figure and reflect it across the x-axis, which I can do, but then it indicates include ordered pairs - that confuses me.
Answered by Penny Nom.
10 hours before 7:15 2002-10-27
From Jessica:
It is evening 7:15. What time would it be 10 hours earlier?
Answered by Penny Nom.
Sanding a wooden block 2002-09-07
From Wanda:
If a wooden block, 2in height, 3in width, and 6in length is sanded and 1/8 of an inch is removed from the top and from the bottom, how much is the volume of the block decreased?
Answered by Penny Nom.
Combination locks 2002-08-17
From John:
How many combinations of three number codes can occur with a standard combination lock? The range of possible numbers is 0-39 which allows 40 different possible choices each turn of the dial. Each combination requires exactly three numbers (i.e. three turns of the dial). E.g. 35-40-5. Allow for reuse of the same number three times e.g.10-10-10. I don't think there is any preference shown for certain number combinations. Can you explain how the total is derived? Someone at the YMCA this week put this question to me and I gave an answer but I am not sure I am right--so I have come to you.
Answered by Penny Nom.
Combinations? 2002-03-16
From Sara:
A combination lock has three dials numbered 0 - 9. Give a mathematical reason why "combination" is a bad name for this type of lock.
Answered by Penny Nom and Chris Fisher.
Counterclockwise 2001-09-14
From Rolanda:
When Descartes invented the coordinate system he decided to number them counter-clockwise. Why?
Answered by Chris Fisher.
A combination lock 2001-04-05
From Ken:
What is total number of combinations possible on a combination lock which contains 3 wheels each numbered 0-9?
Answered by Penny Nom.
When did the man go out? 2000-12-14
From Rajesh:
A man goes out in time between 5 and 6 and when he comes back he observes that two hands have interchanged position. Find when the man did go out?
Answered by Penny Nom.
Three problems 2000-12-14
From Sarah:
Hi, my name is Sarah, and I'm asking this question on behalf of niece who is in secondary two. Thank you.

Q1. What is the angle formed by the hour hand and the minute hand of a 12 hour clock at 5.50pm.


Answered by Penny Nom.
Why counterclockwise? 2000-02-21
From Drew:
Why do the numbers of quadrants in a graph increase in a counter clockwise pattern? Why aren't they numbered increasingly in a clockwise pattern?
Answered by Chris Fisher.
The number of city blocks in a country mile 1999-11-24
From Gloria Hearst:
For years my family has had an on going debate on the number of city blocks in a country mile. We vary from a minmum 8 blocks per mile to a maximum of 12 blocks per mile.
Answered by Nadine Griffiths and Penny Nom.
A goofy clock 1999-11-20
From Kate:
While repairing a watch, a jeweler removed the hands and inadvertently replaced the hour hand on the min. spindle and vice versa. he set the hands to read 2:00pm, which was the correct local time when I picked up the watch. A few minutes later, I noticed that the hands were taking goofy positions. What was the first time thereafter that the watch would show the correct local time?
Answered by Chris Fisher.
Clockwise or Counterclockwise? 1999-10-27
From Tim:
A particle moves around the circle x2 + y2 = 1 with an x-velocity component dx/dt = y
  1. Find dy/dt

  2. Does the particle travel clockwise or counterclockwise around the circle? Why?

Answered by Harley Weston.
Modular Arithmetic 1999-02-04
From Leslie Kupper:
I am trying to do a project on modular arithmetic. I was wondering if there were any websites that include a sample lesson plan on modular arithmetic for any grade level. Let me know where and how to find them. Thanks.
Answered by Harley Weston.
Geometry patterns lesson plans 1998-12-31
From Vicki:
hi,,, my name is Vicki and I am a new 5th grade teacher....

Anyway, I'm supposed to come up with a lesson plan to

  • Explore patterns that result from cominations of "reflections, rotations, and translations of geometric figures.
The plan is to include:
  • writing/metacognition, assessment strategies, interdisciplanary connections, supplemental materials, or textbook, and Bloom's taxonomy level.
Any help you could give would be greatly appreciated.

Answered by Jack LeSage.

Students and Lockers 1998-10-02
From Mike:
There is a row of 1000 lockers.
There is a line of 1000 students.

Student number 1 starts at the first locker and opens all 1000. Student number 2 starts at the second locker and closes every other one. Student number 3 starts at the third locker and goes to every third one, closing the open ones and opening the closed ones. Student number 4 does the same with every fourth locker and so on down the line... After all 1000 students have gone how many lockers are open and which ones are they?

Please help! There is proboly a simple solution but we couldnt figure it out for the life of us. Please let us know how you solve it.
Answered by Patrick Maidorn and Penny Nom.

Hour Hand Movement 1998-04-19
From Chris and Angela Bradley:
My wife and I are haveing an argument over the answer to this question, what is the total number of degrees through which the hour hand of the clock moves in 3 hours and 18 minutes?
Thanks in advance.

Answered by Chris Fisher.
Clock Arithmetic. 1998-03-09
From Joann Dixon:
What is clock mathematics?
Answered by Patrick Maidorn.



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