Mathematics Stack Exchange
Mathematics Stack Exchange

Questions tagged [puzzle]

For questions about the mathematical principles behind puzzle, games, riddles, or their possible solutions. Questions that are not strictly mathematical in nature should be asked on Puzzling Stack Exchange.

Many puzzles, games, and riddles are based on mathematical concepts. This tag is for questions that ask about the mathematics behind a puzzle, game, or riddle, or about the solutions to mathematical puzzles.

If you already know the answer to the puzzle you are posting, you might consider posting your question on Puzzling Stack Exchange, instead. If you do end up posting your question on Mathematics Stack Exchange (MSE), please read the following meta posts on these kinds of questions before asking your question:

If you do end up posting on MSE, please make it clear in your question that you are "puzzling" the community and that you will be answer the question yourself if no one in the community posts your desired solution.

3301 questions
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Simple puzzle from The Moscow Puzzles with wrong solution?

I have a book of mathematical puzzles -- The Moscow Puzzles, edited by Martin Gardner -- and I'm struggling to make sense of the following puzzle. It seems utterly simple, yet the solution given seems completely wrong. Here's the puzzle and solution…
Sam Burton
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1 answer

Puzzle - 123456789 = 100 with three operations?

Given the sequence 123456789: You can insert three operations ($+$,$-$,$\times$,$/$) into this sequence to make the equation = 100. My question is: is there a way to solve this without brute force? (I tried to represent it as a graph but I'm…
sdasdadas
  • 177
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7 answers

Proof that a common brain teaser is wrong (Burning Rope)

There is a common brain teaser that goes like this: You are given two ropes and a lighter. This is the only equipment you can use. You are told that each of the two ropes has the following property: if you light one end of the rope, it will take…
user2879934
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How old was this man and his son?

A man is twice as old as his son. When his son is the same age as his father was when he was twice as old as his son, both of their ages add to 180 years old. What are the ages of the man and his son through both of these time periods? My…
Jason
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Card puzzle involving four cards

You know that all cards are either checker or stripped on the back and have either aces or deuces. How many cards must you flip to answer: is every card that has a checkered back an ace?
most venerable sir
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1 answer

Pure algebra...

There are 5 balls with different unknown weights. We know that the weights of all possible pairs are 16,18,19,20,21,22,23,24,26,27. What are the weights of the ball? Just to verify, is the sum of the weights 53.5. I set three three variable…
most venerable sir
  • 1,689
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3 answers

Weighing puzzle

6 balls, 2 with New York logo. 2 with California logo, and lastly 2 with Texas logo. In each pair, one ball heavier than the other. The heavier ones weigh the same, so do the lighter ones. You are provided a scale. Find all the heavier ones with 2…
most venerable sir
  • 1,689
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1 answer

Number puzzle from NAPLAN practice quiz, I know the answer, but I can't figure out why it is the answer

Consider this puzzle: The answer given by the website is 10 (filled-in already in the picture) But I can't figure out why this is the case. My various thought processes so far have been: The smaller the first number is, the bigger the second…
Siberias
  • 33
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2 answers

Puzzle about convict who chooses length of his imprisonment

This is the puzzle I deal with for few days right now and I can't figure it out. I translated it from other language if I can improve post please comment. In the end of a trial judge sentenced a convict for some years of prison, but he let the…
Yoda
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Riddle about dog running in company of soliders

A group of soldiers march together straight in square formation $50 \times 50$ meters. There is the dog at the back of the formation. Dog starts to run towards the first line of soldiers and then when it reaches front of the formation it starts run…
Yoda
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Is there a faster way to count jigsaw puzzle pieces?

I have a number of old 1000-piece jigsaw puzzles I'd like to sell. I'd like to make sure they are complete first. Is there a faster way to determine whether there are exactly 1000 jigsaw pieces than physically picking up and counting every single…
Emaille
  • 41
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1 answer

The Blind Man and Coins Puzzle

There is a table on which, a number of coins are placed. You also know that there are as many coins with Heads up, as many coins with Tails up. You are blind folded and there is no way to determine which side is up by rubbing, etc. Now you have to…
Srikanth Nakka
  • 217
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2 answers

Riddle that doesn't make sense and makes sense at the same time

How many letters are there to the CORRECT answer to this question? And if you do get the answer please explain how you got it.
Aspiring Mathlete
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Einstein's Riddle Alternative interpretation

I was working with Einstein's riddle yesterday and after some time I figured out a solution. But then I thought. What if the whole neighbourhood is a circle? (If you played GTA San Andreas like Grove street). What if the 5 houses are in a circle and…
John Demetriou
  • 133
3
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2 answers

Find the smallest positive whole number that is equal to seven times the product of its digits

I am helping a kid with the preparation for a mathematical competition. One of the training question is: Find the smallest positive whole number that is equal to seven times the product of its digits They do not provide the answer, but using this…
dd95
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