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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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Great Picnic Puzzle Puzzle (Sam Loyd puzzle)

One of Sam Loyd's puzzles reads: When they started off on the great annual picnic wagon in town was pressed into service. Half way to the picnic ground ten wagons broke down, so it was necessary for each of the remaining wagons to carry one more…
user81362
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six digit puzzle using five restrictions

I have been stumped on this puzzle for a while now. I know the answer, but of course this does not satisfy my need to understand why. Puzzle: Let $ABCDEF$ be a six digit number such that: All digits are different, The sum of the first two digits…
kam
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average no of vertices per triangle in a graph of infinite triangles

An infinite two-dimensional pattern is indicated above. The smallest closed figure made by the lines is called a unit triangle. Within every unit triangle, there is a mouse. At every vertex there is a "sweet". What is the average number of "sweets"…
Nimit
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Continuing with absolute difference of a 2-digit number with its reverse (Kaprekar's Algorithm for 2-digit numbers)

Let $ab$ be a two-digit number($a \ne b$) with its reverse as $ba$, it is simple to check that $|ab-ba|=9|a-b|$. Interestingly, if we continue as $$ |ab-ba|=cd \to |cd-dc|=ef \to |ef-fe|=gh \to |gh-hg|=ij \to |ij-ji|=kl \to …. $$ we will encounter…
Z Ahmed
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Milk pouring problem

12 lts. milk in one can, two measuring cups of 7 and 5 lts, how to get exactly 6 lts? This puzzle was asked our social group by Devidas Naik. The solution could be written in terms of triplets or 3D vectors (C,S,F): C stands for the can S stands…
Z Ahmed
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The Best Way to Choose Spaces for Infection

Consider a 5x7 patch of 1x1 square units. I can choose any 3 of the units in the patch to be infected. After 1 day, an infected square will spread to all the squares adjacent to it (no diagonal spread). My question is: "What 3 squares should i pick…
user773113
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Can a three digit number start with zero?

This is a viral so-called brain teaser where it mentions that the numeric lock is a three digit key. If we solve it using the hints you'll arrive at the answer 042, which is where I'm a little concerned, since I believed a three digit number mustn't…
Chd
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Coin weight puzzle

Let us assume that we have a box of coins which contains 10 normal coins and 11 counterfeit coins. We know that each counterfeit coin is 1 gram less than each of the normal. One coin was taken from the box. If we have a regular scale and we can only…
Giovanni
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A question about drawing a line throught n connected, pairwise intersecting regions.

A friend asked me this: Given n connected regions in space, and any pair of regions has no empty intersection, is it possible to draw a line through all of the regions?
stopwatchingmesleep
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Make an equation true by moving one of the cards

I came accross with this puzzle: There is an equation written in cards so that every card represent a number or a mathematical symbol. Move one of the cards so that equation is true. The equation looks like this: $2 * ( 5 - 1 ) * 3 =…
Mixer
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Would I be able to use mathematics to prove properties that would help me solve this series of puzzles?

I realise that this may be a little different from most of the questions you get on math.stackexchange, so for that I apologize. I also apologize if there's no "one right answer" given the way I've phrased this question. There's a puzzle in the…
Irwin
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Teacher - Parents : How many were they exactly?

At the end of a school year, the 7th grade teachers came to a meeting with a specified number of parents, where a total of $31$ people have participated. Sixteen parents of students put questions to the Latin teacher, with the German teacher spoke…
Mary Star
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rock scissor paper probability

Alice and Bob played 25 games of rock-paper-scissors. Alice played rock 12 times, scissors 6 times, and paper 7 times. Bob played rock 13 times, scissors 9 times, and paper 3 times. If there were no ties, who won the most games? I don't know the…
user2925872
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Guess the color of the cap

I have 3 persons which either wear a white or a black cap. They can only see the color of the other caps, but not their own. White and black caps are eqally likely. As a team, they play a game of guessing their own cap color. If they will win, all…
JohnD
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Using a straightedge, a compass, and a knife to cut a triangular cake into pieces that reassemble into a rectangle

Suppose you are using a triangular cake, a straightedge, a compass, and a knife. Using these, you are only allowed to cut triangular portions from the cake. Can you rearrange these portions (all) to form a rectangle? My strategy worked, but only…
user636268
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