







When are the hands of a clock perpendicular? 
20180111 

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 
20170729 

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 
20170424 

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 
20170218 

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 
20161208 

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 
20161102 

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 
20160315 

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 
20160302 

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 
20151111 

From Jason: Hi,
I can't seem to open my locker cause I forgot the combination, the numbers are 18
Without repeat for 4 number for example 1234 or 2345 for numbers 18 without any repeat. Answered by Harley Weston. 





The weight of a steel block 
20150404 

From Mark: the weight of a steel cube 37 inches X 28 inches X 7 inches Answered by Penny Nom. 





A lost combination 
20140928 

From Kim: I cannot remember my combo to this simple lockbox. It is 3 digits from 09. 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 
20140320 

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 
20131030 

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 
20121224 

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 
20120309 

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 
20120306 

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 
20120227 

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 
20110912 

From JOHN: HOW MANY BLOCK WILL IT TAKE TO BUILD A 28*48 HOME, ON A FOOTER THAT IS DONE ALREADY, I WANT TO GO TEN HIGH. Answered by Harley Weston. 





A lock box 
20110803 

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 punchcode lock box 
20101129 

From Doug: I am a real estate agent that uses punchcode 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.
Rules:
4 digit code
Numbers 09
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 
20101020 

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) coordinates 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 
20100306 

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 pushbutton padlock 
20100117 

From Vince: Hi,
I have a pushbutton padlock using ten buttons (1234567890).
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 
20090821 

From Jamboree: I need to have all the possible combination of three digit between 09, 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 
20090806 

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 
20090404 

From Andrew: I have a 5 digit push combo lock that i forgot the combo for. it has numbers 14 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. 
20090327 

From peggy: my son has locked his ipod and can't remember the combo. He knows it has the numbers 258 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 
20090110 

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 
20081015 

From JESSICA: HI I AM IN GRADE 7 AND FOR MATH HOMEWORK MY TEACHER ASKED US
TO MAKE 8 DIFFERENT TIMES(clocks) AND TELL HIM WHAT THE PERCENTAGE
FOR THE TIME IS.
BUT I DON'T KNOW HOW TO CONVERT TIME TO A PERCENT.
PLEASE HELP ME??!!??
JESSICA
SEVENTH GRADE Answered by Penny Nom. 





A three 09 tumbler lock 
20080922 

From Louis: I recently gave my daughter an old briefcase which uses a three 09 tumbler lock. She set the lock and now she can’t open one side.
Q. Is there a 3 digit combination number generator available to give me the 1000 possibilities?
Thanks,
Lou
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? 
20080814 

From DARLENE: HOW MANY CITY BLOCKS EQUAL 1 MILE IN BIRMINGHAM, AL? Answered by Penny Nom. 





Concrete blocks 
20080618 

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 
20080404 

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 
20080211 

From Alfred: A briefcase lock has 3 columns of numbers each 09. 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 
20080131 

From CARLA: at a certain time i looked at a 24hour 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 
20080102 

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 
20071219 

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 
20071106 

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 
20070829 

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 
20070808 

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 
20070706 

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 
20070701 

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 
20070630 

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 
20070605 

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 
20070521 

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 
20070516 

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 
20070402 

From Gail: How can I get fourth grade students to understand fractions and their equivalents? Answered by Diane Hanson. 





Angle of clock hands 
20070131 

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 
20060716 

From Alejandra: I have a bike lock. It has three columns of the digets 19 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, pushbutton door 
20060620 

From George: We have a 5 digit, pushbutton door look (15). How many combinations are possible without repeating a number in a 3 digit entry code? Answered by Stephen La Rocque. 





A 4digit Combination Lock 
20060309 

From Adam: I have a 4digit 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 
20060118 

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 
20051130 

From Rita: How many blocks are there in a mile in our city of Phoenix, Az.? Answered by Penny Nom. 





A combination lock 
20051003 

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 6^{2} (6x6x6x6) = 1296.
Is this correct?.
Answered by Penny Nom. 





A combination lock has 60 positions... 
20050207 

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 4digit access code 
20050102 

From Missi: I need to find the 4 digit number to access my voice mail. These numbers will be 09 & 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 
20040909 

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 
20040718 

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 
20040517 

From Darrin: I have a puzzle question based on reality. I have a realestate type keybox (Supra) that has 10 digits, 09. 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? 
20040505 

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 
20040502 

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 
20030206 

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 xaxis, which I can do, but then it indicates include ordered pairs  that confuses me. Answered by Penny Nom. 





10 hours before 7:15 
20021027 

From Jessica: It is evening 7:15. What time would it be 10 hours earlier? Answered by Penny Nom. 





Sanding a wooden block 
20020907 

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 
20020817 

From John: How many combinations of three number codes can occur with a standard combination lock? The range of possible numbers is 039 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. 35405. Allow for reuse of the same number three times e.g.101010. 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 rightso I have come to you. Answered by Penny Nom. 





Combinations? 
20020316 

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 
20010914 

From Rolanda: When Descartes invented the coordinate system he decided to number them counterclockwise. Why? Answered by Chris Fisher. 





A combination lock 
20010405 

From Ken: What is total number of combinations possible on a combination lock which contains 3 wheels each numbered 09? Answered by Penny Nom. 





When did the man go out? 
20001214 

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 
20001214 

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? 
20000221 

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 
19991124 

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 
19991120 

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? 
19991027 

From Tim: A particle moves around the circle x^{2} + y^{2} = 1 with an xvelocity component dx/dt = y  Find dy/dt
 Does the particle travel clockwise or counterclockwise around the circle? Why?
Answered by Harley Weston. 





Modular Arithmetic 
19990204 

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 
19981231 

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. Thanks Answered by Jack LeSage. 





Students and Lockers 
19981002 

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 
19980419 

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. 
19980309 

From Joann Dixon: What is clock mathematics? Answered by Patrick Maidorn. 

