Questions tagged [logical-deduction]

A puzzle that requires formal logical deduction to arrive at the solution. This suggests more than merely reasoning through clues to find an answer (you might want [situation] for that).

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Weighing Coins -- a Different Approach

This is a question of my own devising. You have a double pan scale which will tell you whether 2 coins or 2 groups of coins weigh the same or whether one side is heavier than the other side. You have ...
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Identify the truth teller, the liar and the spy

Beginner puzzle This puzzle is intended to be suitable for people who are new to puzzle solving. Clarification: Both experienced solvers and new solvers are welcome to post solutions to this puzzle. ...
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Colombian Sudoku, Cows and Bulls again…

Fill the sudoku on the left so that each column, row, box, and colored box of the same color contain the numbers 1 to 9. The dots show how many numbers in the row or column of the grid on the right ...
542 views

Knights, Knaves, and Spies

I need help understanding this problem. An island has three kinds of inhabitants: knights, who always tell the truth, knaves, who always lie, and spies, who can either tell the truth or lie. You ...
280 views

Largest prime number erroneously erased when finding all primes less than 1000

Chicharron is a lover of mathematics and once wanted to find all primes less than 1000. He did by the following steps below: He wrote all the numbers from 2 to 1000. He circled the number 2 and erased ...
102 views

Brooklyn Nine-Nine: Holt’s Season 2 Puzzle [closed]

I’ve seen several answers to the Weighing Islanders puzzle Captain Holt poses to the squad in Season 2, but I had a different train of thought when solving it. Did anyone use the process of ...
189 views

What is the name of this puzzle type? How to create one? nxn grid where you select n cells with different numbers

I want to create a specific puzzle, but I'm wondering if it already has a name, and if I can find some pointers on how to make it hard. I have a NxN grid filled with numbers going from 1 to N. I want ...
567 views

Fill the triangular grid using the digits 1-9 subject to the constraints provided

Fill the grid using the digits 1-9 four times each. No row or column can contain the same digit more than once. The total of each row and column is provided, as well as clues to the numbers forming ...
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Eliminate some numbers so that each of the three rows contains the numbers 1 through 9 each exactly once

Beginner puzzle This puzzle is intended to be suitable for people who are new to puzzle solving. Clarification: Both experienced solvers and new solvers are welcome to post solutions to this puzzle. ...
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Are you radical enough to solve this SURDOKU?

All "surds" represent whole numbers smaller than 15, and the same number is never used twice with the same index. (It's a sudoku.) Attribution: PUZZLEBOMB.co.uk. Puzzles by @stecks & @...
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Fill the grid subject to product, sum and knight move constraints

Using the numbers 2, 3, 4, ... 19 each exactly once, fill some of the empty squares in the grid with a number so that the product of the numbers in each row is as shown, as is the sum of the numbers ...
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1 vote
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Next date in the future that satisfies the following conditions

When is the next time that a date will satisfy the following conditions: YYYY days from MM/DD/YYYY is also the (DD)th day of a month. Note that YYYY stands for the year. All eight digits of MM/DD/...
1 vote
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A Framework puzzle

About Framework puzzles: A Framework puzzle is similar to a Fill-in puzzle, except there is no rigid crossword-style grid, the tradeoff here being that you get fewer hints for placing (in this case) ...
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Torus Flow Free

Rules: this is a flow free warp puzzle with a 9x9 grid. connect the respective letters together with lines that travel orthogonally through the centers of grid cells. additionally, the sides of the ...
• 405
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3-clue 5x5 Hidato

Rules Fill the grid with numbers 1-25 such that consecutive numbers are adjacent orthogonally or diagonally Try solving it in Penpa There are only about a dozen 5x5 Hidatos with only 3 clues. (...
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1 vote
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Solve the Alphametic: SOUNDS / WOW = ELK

This is a long-division problem in which letters are substituted for numbers. Solve the problem. Determine the number value of each letter; and when the letters in each one have been arranged in order ...
668 views

Bare Bones – a semi-DIY crossword

This is part 64 of the puzzle series Around the World in Many Days. Each part is solvable on its own. Dear Puzzling, This is a semi-DIY crossword. Shade some cells in the grid so that the grid has ...
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New record for minimally clued 7x7 Hidato (now with 6 clues!)

Rule of Hidato: Fill the grid with consecutive numbers such that they connect orthogonally and diagonally. Solve the following three Hidato puzzles. 8 clues 7 clues 6 clues You can solve these on ...
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Current record for minimally clued 7x7 Hidato (16 clues)

Background Back in March, I posted this question on the Puzzling Stack Exchange asking how many clues were needed to create a 4x4 Hidato puzzle with a unique solution. Sometime after this, I took a ...
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How many Friends are there in the circle?

On the island of Friends and Foes, every citizen is either a Friend (who always tells the truth) or a Foe (who always lies). Seven citizens are sitting in a circle. Each declares “I am sitting between ...
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Memorial Day puzzle

In 2025, Memorial Day will be on May 26. Also, in 2026, Memorial Day will be on May 25. Notice that the last two digits of the year and the Memorial Day date in May have just switched places. The same ...
226 views

Flipping DIP switches

About 30 years ago, I bought a memory extension card. At first, I was hesitating: there were 8 dip switches and no manual. Then the owner recalled that 4 switches indicated the memory on the ...
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Off-duty guards on liar island

It's a little-known fact that the guards on Liar Island have to continue their slavish devotion to the individual rules dictating the veracity of their statements. Of course, some always lie, and some ...
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