# Questions tagged [mathematics]

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

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### Unexpected answer to sequence riddle

I've got the following sequence: 11+11=4 12+12=6 13+13=8 14+14=? I've tried multiple approaches: Assuming that the formula is ...
2k views

### 12 piece cube packing puzzle

Consider the following hexacube (made from 6 unit cubes): GOAL: Pack a 3 x 3 x 3 cube using three of these hexacubes plus nine unit cubes. This puzzle comes from: https://puzzlewillbeplayed.com/333/...
479 views

### 25,42=90: find the math pattern

I've got the following pattern: 25,42=90 62,31=92 73,12=? What rule should I apply to 73 and 12 in order to get the answer? With brute force, the answer is but ...
292 views

### Math puzzle: 8,5=100

I'm a bit stuck with this puzzle (image) 8,5=100 10,4=80 16,2=? I've tried 40,52,62,68 but no luck.
425 views

### One more "What does this operator do" question

it is fun to observe that questions like this What does this mathematical operator do? raise more new questions than correct answers! When trying to solve the original question, I came to this new ...
417 views

### Find the next digit in four given sequences

Find the next digit in each of these four sequences: 7 8 8 8 8 ... 3 4 5 2 5 ... 2 1 2 1 2 ... 1 1 9 6 3 ...
962 views

### Can you pack these pentacubes to form a rectangular block with at least one odd side length other the side whose length must be a multiple of 5

This puzzle is part of the Monthly Topic Challenge #11: Now in 3D. Consider the following pentacube (made from 5 unit cubes): It is possible to pack four of these pentacubes to form a 2x2x5 ...
2k views

### Chem-is-try is hard

You are a chemist and ask your coworker to puzzle you. They give you this puzzle and ask you to solve it. LiPSiNArHCaScMgHCaFPSiK
339 views

### Old School Measuring

You have an obscure job in 1600's Brussels. You make reference sticks. You own a high-quality ruler (which are quite rare in that era) and use it to cut lengths of wood or metal to certain lengths ...
251 views

### Median is the mean

Can you divide the numbers 1 to 10 (inclusive) into two sets of 5 numbers each, such that the median of the first set is the mean of the second set, while the mean of the first set is the median of ...
5k views

### Combine 1,3,3,7 to get 10

I tried lots of combinations but could not find a solution. Each number has to be used exactly once, the allowed mathematical operators are Addition: + Subtraction: - Negation: (unary prefix) - ...
149 views

### 2023 From Numbers 1-15

Using the numbers 1, 2, 3,..., 15, in that order, how can you make the number 2023 using the +, -, $\times$, and $\div$ operations. (You can use as many parentheses as you want.)
897 views

### 2023 Squared From Squares

Without moving or removing any number, replace each of the triangles by either $+$, $-$, $\div$ or $\times$, and insert as many sets of parentheses as you want, in order to make the following equality ...
2k views

### What does this mathematical operator do?

The solution to this puzzle is one I came up with when working on this puzzle: What is the answer of this math puzzle? For two natural numbers a,b, can you figure ...
1 vote
436 views

### Just one symbol that answered a question

I was doubting whether or not to go on vacation. So I asked someone if I should go. The answer was given on a piece of paper, with only the following symbol: ∟ What did it mean? Added hint:
1k views

### What is the answer of this math puzzle?

One of my friend brought this simple-looking math puzzle to me, but it was harder than it seems. I tried several ideas including simple arithmetic operations, and even considering base-n. ...
530 views

### Find the right key as fast as possible

I have a number of keys on my keyring and want to find the correct key as fast as possible. Unfortunately, all the keys look the same. However, I can see if the teeth are turned the same or opposite ...
774 views

### Replacing Untold Billions

First: Assume Earth's population is 8,037,860,611 and they have ID numbers 1 through 8,037,860,611 You make a set of cards numbered 1 through 8,037,860,611 A robot goes to each person in turn and ...
1 vote
192 views

### The Angel Problem - Sticker Devil Variation

So If you are aware of the angel problem, I propose a Variant: we introduce the Sticker Devil: A normal devil, with the added ability to sacrifice his turn to color any and all White Tiles that are ...
579 views

### Measure the rod

You are given three meter scales A, B, and C are shown in picture given below. The scales are however, quite unique in their properties as they have different numbers of division per meter. You are ...