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Questions tagged [mathematics]

A puzzle strongly related to mathematical facts and objects, or whose solution needs serious mathematical arguments. General mathematics questions are off-topic but can be asked on Mathematics Stack Exchange.

10
votes
1answer
877 views

Fill in the number. Not as straight as it looks

The square below is missing a number: You have four options: 32 4 16 22 Please explain your answer. HINT:
1
vote
1answer
93 views

Create a 3x3 Magic Square that uses integers from -10 to -2

I've never used this before but i'm having trouble with this. Create a 3x3 Magic Square that uses integers from -10 to -2. By the way, this is a weird magic square since diagonals don't need to ...
14
votes
9answers
7k views

Salesman's claim for mechanical keypad lock - 5 buttons and 545 combinations!

A company makes mechanical keypad locks. The keypad is a set of five buttons arranged vertically. O O O O O The buttons are quite close together. Once a ...
11
votes
3answers
2k views

Coin removal problem

I have a slight variation of the coin flipping problem. There is a line of $n$ coins on the table; some of them are heads up and the rest are tails up, in no particular order. The object of the ...
1
vote
2answers
130 views

5 subjects and their marks

The following partially-filled table shows the marks scored by 5 students named A, B, C, D and E in five different subjects, namely P, C, M, B and S. The marks scored by all students in all subjects ...
3
votes
1answer
84 views

Creating my climbing wall

[based on a true story] I have here some climbing holds that I've made. There are two relevant parameters: The angle on the top, and The thickness, as shown. Now it is definitely the case that $...
0
votes
1answer
128 views

puzzling one for my 11 year old and myself [closed]

$\frac{1}{4}$ of the marbles in a box are blue. There are $24$ more red marbles than blue marbles in the box. The remaining $32$ marbles are yellow. How many red marbles are in the box?
2
votes
0answers
73 views

Sets and subsets [closed]

Assume a set of numbers $S$ which must satisfy four conditions. (1) Partition this set $S$ into three subsets $U_1$, $U_2$, and $U_3$ such that the sum of the largest subset is as small as possible (...
-1
votes
2answers
150 views

Who joined when?

An institute runs batches training students in C#. A new batch starts on the 1st of every month and every batch lasts for exactly 3 months (thus at any given time, the students of exactly 3 batches ...
31
votes
2answers
631 views

lolcatz can haz ur infinit cheeseboard

This is a problem on an infinite chessboard with pieces called lolcatz. They can move like queens or knightriders, but have a strange disadvantage... ... you've never heard of knightriders? Well, ...
5
votes
3answers
171 views

Buzz Buzz Busy Male Bees

A male bee is born from an unfertilized egg, a female bee from a fertilized egg. In other words, a male bee has only a mother, whereas a female bee has a mother and a father. How many total ancestors ...
7
votes
3answers
624 views

No spanish required

Each letter represents a digit, so what is Mucho and Poco (although who's to say?) ...
-2
votes
2answers
73 views

Schedule of a business [closed]

With a group of 8 students you have set up a small business with which you help a customer every day during the holidays to clean up his computer and to redecorate it. For the next day there are 12 ...
-1
votes
1answer
425 views

Why does 12/2 = 7? [duplicate]

Here's a quickie while I work on the fourth floor of the Puzzle Dungeon. It's going to be here within the next two days, probably. Find a way to divide 12 by 2 so you get 7. There are several rules: ...
6
votes
1answer
129 views

The town of Concentrië

Here you see a water map of the town of Concentrië. There are eight channels that run from the central boathouse of the city in a star shape. There are three canals that lie concentric around the ...
11
votes
3answers
823 views

The 1-expression

A "1-expression" is a formula in which you add ($+$) or multiply ($\times$) the number 1 any number of times to create a natural number. Parentheses are allowed. For example, you can create $22$ as ...
2
votes
15answers
3k views

Just One Line! Really? [closed]

Add ONLY ONE line (does not have to be a straight horizontal line or in other words, doesn't need to be an axis aligned to the equal sign) to make the equation below true : EQUATION : $...
5
votes
4answers
438 views

Grandpa’s baseball cards [closed]

One day at a family reunion we found a bunch of baseball cards in Grandpa's basement. Grandpa said we could split them among all the grandkids. There were 5040 cards in all, so each of us got a lot of ...
-1
votes
1answer
121 views

Residential society [closed]

In a residential society, there are 120 people who either consume only tea or only coffee. Of those 120 people, 25 are children (which includes male as well as female children), and 78 consume tea. ...
0
votes
2answers
119 views

Ranking And Average

Four athletes A, B, C and D are evaluated on four different parameters – S, A, I and T. Further it is known that: I. Each athlete was given a score, which was an integer between 4 and 10 (both ...
3
votes
1answer
295 views

It's almost a cube

What is the next number in this sequence? 7, 10, 12, 19, 20, 30, _____ Note: I added another number as at first the pattern fit this too well. Hint 1:
1
vote
1answer
186 views

Voting System Puzzle

Answer Questions 79 to 82 on the basis of the information given below: The year is 2089. Beijing, London, New York, and Paris are in contention to host the 2096 Olympics. The eventual winner is ...
4
votes
1answer
123 views

Length of the Sequence

There's a lot of number sequence based questions on this site. So I'm going to mix it up a little bit. This sequence will repeat eventually. You need to find how many numbers are in the sequence ...
5
votes
1answer
449 views

Solve this puzzle. I created for my friend for FUN :)

My friend is very good at puzzles. so i thought of creating one by myself and try to see if he can solve. Finally I succeeded and he gave up. Interested people can try. Hint: use all four arithmetic ...
0
votes
3answers
300 views

Rullo solving strategy for 2-4

How to eliminate/nominate candidates without guessing? For the 3s it's quite easy because of the odd numbers but how to get further?! For thoose who don't know the game, here's a short introduction:...
2
votes
1answer
171 views

Master and Slave versus Bob: easy version

Continuation of: "Sub-puzzle: Master and Slave versus Bob the Violent but Honest Psychopath" Continued in: "Master and Slave versus Bob: hard version" Previously I described a game that is played ...
10
votes
17answers
5k views

100 using only 5 number of digits

This is a problem from Martin Gardner. For each digit $1\leq d\leq 9$, make 100 using exactly five number of $i$s. Any operation is allowed, brackets as well. For $i=1,2$ I have a solution: $$100=...
2
votes
1answer
144 views

Row of alternating coin

I stumbled upon a mathematical puzzle that goes like this: You have 2n coins that alternate between head and tail. For example, if n=3, then it looks like H T H T H T, where H = head and T = tail. To ...
8
votes
2answers
267 views

A CrossNumber puzzle with a twist

Here's an interesting puzzle which I discovered the solution to yesterday. The eleven grid entries in increasing order are $A, B, C, D, E, F, G, H, I, J, K$, and you are given the following hints. ...
1
vote
1answer
234 views

What is the value of X?

24 6 63 132 4 14 23 x 17 The answer is either : 21, 14, 3 or 2
1
vote
1answer
225 views

Master and Slave versus Bob: hard version

Continuation of: "Sub-puzzle: Master and Slave versus Bob the Violent but Honest Psychopath" and "Master and Slave versus Bob: easy version" The hard version is identical to the easy version (see ...
1
vote
3answers
294 views

Sub-puzzle: Master and Slave versus Bob the Violent but Honest Psychopath

[I created this as a sub-puzzle to "Strategy to beat the Casino reversed", that has been sitting unsolved for months. You may wish to read that puzzle first, but this is self-contained. My answer to ...
4
votes
1answer
150 views

More Email Shenanigans

I don't know how these people know my email address, but after the (still unsolved) shenanigans of the Interesting email I received? I got... yet another email. This one was of a Google Drive document ...
4
votes
0answers
260 views

My brain froze trying to solve this [closed]

Try to figure out the missing numbers!
5
votes
2answers
209 views

Using 20, 17, 16, 8, 7 to make 9

You can use $+, -, \times, $ or $/$ (namely $\div$). Use all five numbers (20, 17, 16, 8, and 7) only once to make $9$. From what I've been told there are $4$ answers. The only one I've been able ...
2
votes
1answer
130 views

Some Really Confusing Math

I was talking to a co-worker this morning and he stated that he was able to make both of these statements true using only $1, 3, 5,$ or $ 7$. He then proceeded to tell me: $1 = 5$ $2 = 4 + 7$ $3 = 1$ ...
3
votes
2answers
432 views

Which polygon is the one?

There is a unit-radius circle and you must form a polygon all of whose vertices are located on the circle, such as below: What is the biggest possible value of the sum of squares of side lengths of ...
5
votes
2answers
1k views

Did Grandpa count correctly? Another Grandpa Mystery

Grandpa just returned from a long trip. He started telling me about his adventure in a wild place. " I saw animals", he said. "Three different kind" "Just for fun I counted their limbs" "...
21
votes
9answers
5k views

Google's 20th Anniversary: Make 20 using 6 0 0 6 1 3

Belated 20th Happy Birthday to Google (600613)! Challenge: Use 6, 0, 0, 6, 1, 3 to make the number 20. Rules: Use all numbers, in that exact order. Allowed operations: +, -, x, /, sqrt, (); no ...
7
votes
6answers
3k views

Use 6, 5 and 3 to make 57

Assemble a formula using the numbers $5$, $6$, and $3$ in any order to make $57$. You may use the operations $x + y$, $x - y$, $x \times y$, $x \div y$, $x!$, $\sqrt{x}$, $\sqrt[\leftroot{-2}\uproot{2}...
13
votes
9answers
2k views

Use 0, 5, 7 and 1 to make 89

Assemble a formula using the numbers $5$, $0$, $1$, and $7$ in any order to make 89. You may use the operations $x + y$, $x - y$, $x \times y$, $x \div y$, $x!$, $\sqrt{x}$, $\sqrt[\leftroot{-2}\...
1
vote
2answers
103 views

Is this possible ( - ) + + - - - = 100 I can do many other way

Insert the numbers 1-9 inclusive each only once into the calculation to arrive at the answer 100. ( - ) + + - - - = 100 Is this possible?
0
votes
2answers
202 views

Can you solve the riddle

Can you solve the mathematics puzzle?
1
vote
4answers
105 views

Air Miles Challenge

This isn't my own creation, it's an exercise that my partner had to do during a work exercise and seemed interesting to share here. You've been given 86,400 Air Miles to explore the world and there'...
14
votes
2answers
439 views

Cross-number puzzle

ACROSS: A. a square C. a multiple of N Across E. (C Down) $\times$ (I Across) G. a square root of A Down I. a square root of D Down J. (J Across) $\times$ (K Across) = (F Down) $\times$ (M Down) ...
6
votes
2answers
165 views

A Crucial Delivery

Planet Earth has been at war with the nefarious aliens of Planet XYZ for a while. The front lines are on Planet XYZ, and you, being Earth's lead scientists, need to find a way to get vital information ...
-2
votes
3answers
134 views

Perkin's age problem [closed]

Perkin and Poise's combined age is 22 which is 3 years more than the combined age of Perkin and Pootle which is 2 years more than Poise's and Pootle's age combined. The question is - In how many ...
5
votes
4answers
176 views

The athletes puzzle [closed]

Athletes arrange themselves into $x$ rows and $y$ columns. We pick the tallest of every column and name the shortest of them A. We pick the shortest of each row and name the tallest of them B. ...
12
votes
5answers
4k views

Hard 4x6 chocolate bar Riddle

You have the following 4x6 chocolate bar. The question is what is the least amount of cuts you have to do in order to create 24 pieces of 1x1 chocolates. the cuts can have any shape they want as long ...
8
votes
4answers
354 views

A “Find the Path” Puzzle

I invented a puzzle, inspired by Simon Tatham's Portable Puzzle Collection. Is there anything that it could improve on? Was it too easy, or was it too hard? Anything I could add? What must I call it? ...