Puzzling Stack Exchange
Puzzling Stack Exchange

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.

Mathematics is the study of abstract topics as:

and also has applications in computing and finance.

There is a selection of mathematical puzzle-making tools at A collection of Puzzling Tools on the meta site.

Mathematical problems, as opposed to mathematical puzzles, are considered off-topic. Consider posting them on our sister sites Mathematics Stack Exchange or MathOverflow instead (depending on level).

Puzzling.SE uses MathJax to format any maths in posts.

4730 questions
127
votes
12 answers

Paying the Troll toll

You are on your way to visit your Grandma, who lives at the end of the valley. It's her birthday, and you want to give her the cakes you've made. Between your house and her house, you have to cross 7 bridges, and as it goes in the land of make…
Shevliaskovic
  • 2,204
  • 4
  • 20
  • 26
66
votes
8 answers

A walk of 3000 meters, but one foot has moved more, how so?

My math teacher has struck again. Here's his newest riddle: Today I went for a normal walk of 3000 meters. One of my feet had to move exactly 3000 meters. However, the second foot moved 3100 meters. Can you justify how did that happen? Edit: I am…
Paul Karam
  • 2,221
  • 1
  • 15
  • 28
48
votes
11 answers

Function that is 1 for all positive integers but 0 at 0

A friend of mine had a simple question (at least to state) that I thought I would share: can you, without the use of indicator functions, find a(n) (elementary) function that satisfies \begin{cases} f(n) = 1,& n \in \mathbb N \\ f(0) =…
Therkel
  • 685
  • 1
  • 6
  • 13
48
votes
11 answers

6, the magic number

Here's a fun (albeit difficult) one: Make these equations true using arithmetic operations: 1 1 1 = 6 2 2 2 = 6 3 3 3 = 6 4 4 4 = 6 5 5 5 = 6 6 6 6 = 6 7 7 7 = 6 8 8 8 = 6 9 9 9 = 6 For example: 6 + 6 - 6 = 6 (I hope I did not spoil some of you…
ThreeFx
  • 2,456
  • 4
  • 18
  • 24
38
votes
10 answers

Unsolved Maths Problems as Puzzles

On an internal wiki at work, people sometime post puzzles similar to those found on this website. Most of the questions are formulated as a story or word problems, but can be expressed mathematically and become simple to solve. I had an idea for a…
MikeS159
  • 489
  • 4
  • 6
34
votes
2 answers

What bases make this number square?

For what values of $x$ is the number $121$ a square in base $x$? This is a very easy question, but I still think it's pretty fun. Perhaps it's something to pass on to younger people who are taking algebra.
blakeoft
  • 1,519
  • 11
  • 13
33
votes
8 answers

Will the ant reach the car?

A car starts distance 1 from a wall then drives away at constant speed $ c $. There is a length of elastic tied between the wall and the car. Remarkably this doesn't affect the motion of the car (in reality the tension would slow the car).…
Colonel Panic
  • 2,226
  • 2
  • 19
  • 28
33
votes
3 answers

Maximum time for ants to fall off stick

Suppose there are $n$ ants on a stick which has length 1. At any time, the ants may be facing left or right, the initial directions of the ants are arbitrary. Each ant can be modeled as a point in the stick. At time 0, all ants start moving in the…
justhalf
  • 6,014
  • 2
  • 31
  • 49
31
votes
2 answers

An easy trillionth power

Hardy was revisiting Ramanujan and this time arrived in taxicab number 1792. He remarked that this number seemed rather dull. Ramanujan replied, "It is very interesting, it is the product of the first six digits of a trillionth power." Please find a…
Tom
  • 70,468
  • 4
  • 249
  • 361
28
votes
1 answer

Use three 10's to create 950

Here is an interesting puzzle that I found: You have three 10's. It looks like this: | 0 | 0 | 0 Add one stroke to the diagram to create 950.
WarpPrime
  • 381
  • 3
  • 8
27
votes
2 answers

Robot ants that stay forever on a rod

You can place any positive number of robot ants on a long rod and set each of them to move left or right starting at time $0$. You can set any positive speed for each ant. When 2 or more ants meet, they turn around. When an ant reaches the end it…
Eric
  • 6,488
  • 17
  • 58
26
votes
7 answers

The population of Barberland

The Barberland Institute of Trichodemographic Research has published the following results: Nobody in Barberland has more than 1,000,000 hairs. No two inhabitants of Barberland have the same number of hairs. Nobody in Barberland has the same number…
GOTO 0
  • 13,549
  • 6
  • 47
  • 92
25
votes
1 answer

Maths equation: 357568588-11 = ~357568584.858

Move one line and make this true: $357568588-11 = $ ~ $357568584.858...$ No cross through the "=" sign stuff. Hint: It can be ANY line
Rohit Jose
  • 2,583
  • 7
  • 26
25
votes
2 answers

2017 is the 1st prime satisfying three conditions. What is the 2nd?

$2017$ is prime, and so is $(2017+1)/2=1009$. $2017$ can be written as $a^2 + b^4$: $2017 = 44^2 + 3^4 = 1936 + 81$. $2017 \equiv 2 \bmod 31$. What is the next prime (if any) that satisfies these same three conditions?
Joseph O'Rourke
  • 361
  • 2
  • 7
25
votes
4 answers

Make the equation true by only drawing a single straight line

Fred has a puzzle. The instruction sheet, which is separate from the equation,simply says: "Make this equation true. You may ONLY draw ONE, PERFECTLY straight line". The equation is all alone on a blank piece of paper and reads: …
Theodosius Von Richthofen
  • 379
  • 1
  • 3
  • 9
1
2 3
…
35 36