# 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.

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### How heavy each of these 7 creatures weights?

I was thinking about creating some riddle for TED-ED and somehow I came up some math riddle something like that: "A group of seven creatures weights together 1000 kg, the largest one and second ...
4k views

### Prime Number Snake

Place numbers 1 to 100 in the cells of the 10 x 10 board below in such a way that consecutive numbers occupy neighboring cells (either horizontally or vertically). Shaded cells should contain only ...
436 views

### The seven letter word

Don't worry, I won't let you overflow. Is anyone operating on you? I won't let you overflow by that. Do you want to link yourself? I won't let you overflow by that. Is there an ...
66 views

### Next palindrome date and time

Date and time is formatted as "hh:mm:ss DD:MM:YY", where hh is a 24 hour clock, mm are minutes, ss are seconds, DD are days, MM are months and YY are the last two digits of the year. All terms can ...
316 views

### Prime number snake (2)

This question is inspired by prime number snake. In the following grid, you have to place a number snake of numbers 1 to 100. Consecutive numbers have to go into neighboring cells. Numbers in grey ...
96 views

### Previous palindrome date

2nd of February this year will be a palindrome date, because 02/02/2020 reads the same forwards and backwards. But when was the previous palindrome date?
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### Modular exponentiation. Why all different? [closed]

Why is it if we use 1 2 3 4 mod 5 and we take x^3 of this numbers, we come to: 1 3 2 4 (all numbers are different as you can see)
85 views

### I love books and to read them and count them but I didn't have enough time! [closed]

So, I have ten books. My friend from Indonesia gave me ten and my friend from New York gave me 75. Then my sister took 4 but my brother got 1 back. Then I sold 15 to my friend from India and 5 to my ...
109 views

### How to solve how many times the ball collides with the corner [closed]

In the cartesian coordinate system, four points (0, 0),(20, 0),(20, 19) and (0, 19) are used as vertices to draw a rectangle. At first, a ball with negligible size is at the (0, 0) point. It then ...
336 views

### Calculators are bad at Arithmetic

Consider the following fraction: 17/30 Punch this into a calculator and you'll get the following answer: 0.566666666666666666666666666667 However, I disagree. I say the answer is most ...
1k views

### The missing number

The integer numbers from 1-30 are mutually communicated to you one by one in a random order (one number about every 5 seconds). However exactly one of those numbers is not communicated. What is a ...
215 views

### Locations on the Earth that are all separated by the same distance

What is the maximum number of distinct locations you can select on the surface of the Earth, such that the distance between every pair of locations is the same? Assume that the Earth is a perfect ...
3k views

### Is it possible to divide a square into convex pentagons?

I have seen this question on reddit (r/math's chatroom - to be specific). No one has answered it yet, so I thought I would pose the same question here. The only discovery I made that is worth ...
289 views

### Is it possible to put the numbers into circles?

This topic is motivated by the trolley813's answer on my question. Question. Is it possible to put the numbers $1,2,3,...,23$ in circles so that the sum of the four numbers on $9$ sides of $3$ ...
187 views

### Put the numbers $1, 2, …,16$ in circles

Put the numbers $1, 2, 3, ..., 16$ in circles so that the sum of the four numbers on each side of the triangle should be equal.
892 views

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### A Grid With the Products of Its Rows and Columns are the Same Set of Numbers

Lets say there is a $3 \times3$ grid that is filled with the numbers $1,2,3,...9$ Can the numbers be arranged so that the products of the columns are the same set of numbers as the product of the rows ...
107 views

### Sum of All the Others

There are ten different 10-digit decimal fractions, one of them being equal to the sum of the other nine. If each number has 10 unique digits, not counting the 0 before the decimal point (for example ...
617 views

You are given several pieces of paper which are as follows: (Unfortunately, a textual rendering is very difficult with this puzzle, so if someone can offer a suggestion on how to do it, that would be ...
2k views

### How to solve Rubik's Cube using mathematical formulas? [closed]

I am trying to solve Rubik's Cube, but it took one month for me when I started. Are there any mathematical formulas, rules and tips for solving Rubik's Cube in less time (i.e. minutes)?
126 views

### Make $\pi$ using 2 0 2 0 in this order

How can you make $\pi$ using 2, 0, 2, 0 in this order? Allowed operations: +, -, x, ÷, ! (factorial), exponentiation, parentheses.
64 views

### Painting a grid with 3 colours such that there are no right-angled triangles of one colour

What is the largest rectangular NxM grid (by area) that can be painted with 3 colours, such that no three cells of the same colour form a right-angled triangle. N and M must be 4 or greater. We only ...
182 views

### Find the value of $\bigstar$: Puzzle 10 - Uncertainty

This puzzle replaces all numbers with other symbols. Your job, as the title suggests, is to find what value fits in the place of $\bigstar$. To get the basic idea, I recommend you solve Puzzle 1 ...
265 views

### Find the value of $\bigstar$: Puzzle 9 - Options

This puzzle replaces all numbers with other symbols. Your job, as the title suggests, is to find what value fits in the place of $\bigstar$. To get the basic idea, I recommend you solve Puzzle 1 ...
217 views

### The Train and The Cyclist [closed]

A railway track runs parallel to a road until a bend brings the road to a level crossing. A cyclist rides to work along the road everyday at a constant speed of 12 miles per hour. He normally meets ...
4k views

### Are all balls the same weight?

There are 10 balls which come in two possible weights. Using a balance scale at most 3 times, determine whether all the balls are the same weight or not. Notes: I got this riddle from this ...
289 views

### A 3x3 grid of numbers with unique row and column medians

Can you place every number from 1 to 9 into a 3x3 grid such that the median of every row and column is a unique value? The median of a row is the number that is greater than one number and smaller ...
202 views

### Ten, nine, eight, seven, six, five, four, three, two, one

Some of us already did, and some of us are going to end the years with the word "teen" in it soon, for another 94 years. So let me ask the question: How many distinct numbers can you produce with ...
154 views

### Two dice with same probability for each sum mk2

Inspired by Two dice with the same probability for each sum? To cheat in a game of sums, you get yourself a pair of magic dice. That pair behaves in a wonderful way where each individual die is fair (...
254 views

### A 4x4 grid of numbers with unique row, column and diagonal ranges

Can you place every number from 1 to 16 into a 4x4 grid such that the range of every row, column and two main diagonals is a unique value? The range of a row is the difference between its maximum and ...
856 views

### A Guide to the Number Rotation Puzzle

This is an extension of What is the strategy to solve Simon Tatham's Twiddle? in that it explicitly goes beyond the default gamemodes of Twiddle The Number Rotation Puzzle (NRP) is a combination ...
124 views

### A 3x3 grid of numbers with unique row and column ranges

Can you place every number from 1 to 9 into a 3x3 grid such that the range of every row and column is a unique value? The range of a row is the difference between its maximum and minimum values (...
52k views

### A camel transporting bananas

A somewhat well-known puzzle is described as such: You have a pile of 3,000 bananas. You wish to transport them to a place 1,000 miles away on the back of a camel; however, the camel can only carry ...
335 views

### Four dice puzzle: Postscriptum

This continues (and completes) the sequence of four dice puzzles: Four dice puzzle: 2,2,4,5 Four dice puzzle: What's the best throw? The days go by and Damiano is still throwing his four dice. He ...
This continues Damiano's puzzle "Four dice puzzle: 2,2,4,5" Damiano keeps throwing his four dice. After a lot of throwing and thinking and working, he has determined for every throw $a,b,c,d$ of his ...