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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18
votes
2answers
2k views

Math logic Triangle

Rules Arrange numbers from 1 to 15 to the white triangles. A op B = result Green triangle means 2 numbers of its side are adjacent numbers. (-) means find the difference (/) means divide the bigger ...
18
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4answers
2k views

Past, Present and Future

There are 3 gods, named Past, Present and Future, who all look identical. They sit in a throne room, with one in the middle, the others on the right and left. You are allowed to ask them a series of ...
18
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2answers
2k views

True-False Examination

Alice, Bob, Chloe and David took a 10 question true-false exam; every correct answer of a question is $1$ point. Their answer sheet and the result is shown as below: So what is David's total ...
18
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6answers
2k views

Pursuit Problem: Mutineer trapped on an island

You are a pirate. One of your crew ran off in the night, swam to your secret island, and dug up your life's treasure. You need to capture her. You may deploy $n$ pirate ships to patrol the boundary ...
18
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1answer
924 views

Rearrange the Sentences, Cross out the Wrong One, Fill in the Blank, and… Do Some Logic!

Introductions 1. Rearrange the sentences below into a good conversation! Alice: Hi Bob, how are you? Alice: I'm fine too, but my school kinda sucks. Bob: And how about you, how ...
18
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1answer
856 views

A Total Masyu puzzle

In a Total Masyu puzzle, one must draw a single loop through the centres of some cells according to the following rules: The loop may only travel horizontally or vertically, never diagonally; all ...
17
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17answers
12k views

If this were an answer, what would be the question?

Heading down to the city of Thebes, you encounter a Sphinx who stops you in your journey and speaks to you. The Sphinx has a riddle for you: if you can solve it, she will let you pass; if you fail, ...
17
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8answers
4k views

Infinite precision

The man tells you, "To enter the door of infinite precision, you must complete all of these tasks perfectly: Hold in front of me a baby that is exactly two days old. Bring me a metal object that ...
17
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10answers
1k views

Communicating Information about Cards

Seven cards, numbered $1,2,3,4,5,6,7$, are distributed randomly among three people: Rand gets one of them, Deusovi gets three of them, and Gareth gets three of them. All three know what the seven ...
17
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2answers
2k views

Find the missing piece

One day I got a paper from my courtyard with the center portion missing. Here is what the poster looks like: I have made some pieces of paper so that I can stick one to the center of the poster. ...
17
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3answers
5k views

Which two students spoke wrongly? [duplicate]

A teacher wrote a large number on the board and asked the students to tell about the divisors of the number one by one. The 1st student said, "The number is divisible by 2." The 2nd student said, "...
17
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4answers
782 views

Constructing interesting “Don't Know - Don't Know - Now I know!” type puzzles

The professor has a piece of hidden information $C$. Alice is given an envelope containing information $A$, Bob is given information $B$. It is possible to deduce $C$ from $A$ and $B$. The ...
17
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6answers
2k views

Abby and Bobby and three numbers on the blackboard

Abby selects a non-negative integer $A$, and Bobby selects a non-negative integer $B$. They then both tell their number secretly to Summy. Summy writes the numbers $5$, $8$, and $15$ on the ...
17
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3answers
390 views

Is $s$ larger than the radius of circumscribed circle?

In the figure, showing a square and an equilateral triangle, is $s$ larger or smaller than the radius of the circumscribed circle?
17
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3answers
3k views

Binary Minesweeper

This Puzzle is a form of the classical MS Minesweeper which keeps popping into my head. In Minesweeper, a 2D grid is filled with mines and numbers whereas each number represents how many of its 8 ...
17
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8answers
6k views

When to be sure that we have counted all the squares in such problems

My first question: how would one solve such problems (in general)? What should be the general technique? My second question: When to be sure that we have counted all the squares in such problems?
17
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6answers
6k views

A death at a restaurant

You are a mafia leader and because of mysterious recent developments, you had to call the meeting of heads which is happening right now at your's cousin restaurant. The problem is, after the opening ...
17
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2answers
1k views

Equal queens in every aspect

It is asked that you place $12$ queens on a $5$x$5$ chess board so that every queen can see the same number of empty squares. For the purposes of this puzzle, a queen can see any square on ...
17
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4answers
2k views

Can anything be deduced from the statement “If I am a truth teller, the other two are liars”?

There is a scenario which goes along the following lines: There are three friends. The friends are either truth tellers, or liars. One friend makes the statement: "If I am a truth teller, the ...
17
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3answers
2k views

Two brothers, two watches

Two brothers, Jack and Joe, were born in May. One was born in 1932, and the other, a year later. Each brother owned a watch, which was previously possessed by their father. Considering their age, ...
17
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5answers
3k views

Help me, I hate squares!

There is $5$x$5$ equidistance matrix dot given as below; You need to remove dots from the figure where it will be impossible to form a square by drawing lines between dots at the end. So what is ...
17
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2answers
2k views

How to solve the next field of this Kenken-Puzzle by logic?

First of all here is the spoiler free Kenken-Puzzle for everyone who likes to solve this on her/his own. Now here is how far I come with this, but now I struggle a lot. What I am looking for is only ...
17
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5answers
1k views

Again! 6 prisoners, 2 colors, one mute

After that last game, the warden didn't like that they escaped. So he made them all play again. Like before, they know there are 6 prisoners, 3 red hats and 3 white hats. They know one prisoner is ...
17
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4answers
420 views

The Djinni, the Marid and the Oracle (working title) :P

Although I like this puzzle, I'm still fairly new to this site and I've never tried to write one like this before. I think it may be a little too long, a bit too easy and some of the spelling and/or ...
17
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3answers
2k views

Mutation of aliens

In the image you can see twelve mutation chambers (A to L). Each alien on the left side of the aliens goes through the three mutation chambers of its right side. The alien on the right side is the ...
17
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1answer
1k views

Sudoku with only 8 predefined numbers

Have fun with my self-made Sudoku puzzle. Solve this Sudoku puzzle using the standard Sudoku rules: Fill any row, column and bold-framed area with the numbers 1 to 9. Hint: It is not as difficult as ...
17
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9answers
1k views

Agent 001's faulty delivery box

There are 10 agents living at their respective homes. They used a secret mailing system that sends one box at a time, but it is now spoilt. Now, it functions as follows: It counts the number of ...
17
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1answer
898 views

Farm dimensions

Here is a question I was given during an interview a few years ago. There was a farmer who had two daughters. One day he was considering giving his farm to his girls. He took his first daughter, ...
17
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1answer
2k views

The Pirates of Beal Isle - very long logic grid puzzle

Story Let me tell ye a tale: Somewhere northeast o' the Bahamas there be a tiny scrap o' rocks stickin' up out o' the sea known as Beal Island. It be a barren, rocky place, and no man ever called it ...
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5answers
1k views

100 Prisoners' Names in Boxes - Save them all!

This puzzle is based on 100 Prisoners' Names in Boxes: Names in Boxes The names of 100 prisoners are placed in 100 wooden boxes, one name to a box, and the boxes are lined up on a table ...
17
votes
1answer
319 views

Diabolical Deceptions: A 333rd Birthday Tribute to J.S. Bach

Johann Sebastian Bach is one of the most famous composers from the Baroque period. If he was still alive today, he’d be 333 years old. So, let’s celebrate 3 of his most famous works with a 33x33 loop ...
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3answers
989 views

Names of Physicists Problem

This problem has been vexing me all day. It comes from an old IQ test. Note that while the test says not to discuss the problems on it in order to maintain its integrity, the test itself closed years ...
17
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1answer
573 views

Middle out: A puzzle that won't behave

Ah, jeez. You'd think making puzzles was easy. What kind of fool thinks he can turn up and instantly turn in a working puzzle on his first try? I've been checking my pocket calculator and rolling die ...
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9answers
7k views

Salesman's claim for mechanical keypad lock - 5 buttons and 545 combinations!

A company makes mechanical keypad locks. The keypad is a set of five buttons arranged vertically. O O O O O The buttons are quite close together. Once a ...
16
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2answers
2k views

Blind Person Ball Game

You are blind and your friend presents you with 6 equal balls of which 3 are red and 3 are green. You friend challenges you to game to find a green ball. You must select 3 of the balls and your friend ...
16
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4answers
30k views

How to solve this IQ test puzzle with arrows and pied squares?

What is correct answer for this IQ task and why?
16
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3answers
2k views

Four buttons on a table

I was asked lately (in an interview) to solve this puzzle, which is similar to the 4 cups on table puzzle. In a certain room there is a rotating round table, with 4 symmetrically located ...
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3answers
3k views

Which lorry is carrying drugs?

Five lorries are parked in a French layby, having recently come off the ferry at Calais. The police know that the lorry headed for Lisbon is smuggling drugs, but they're not sure which one it is. All ...
16
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2answers
2k views

It'd be on an infinite board, but he can't fit one in his hideout

This is a fairly easy one (at least as this website goes) with a premise taken from the Reader's Digest Book of Puzzles & Brain Teasers. The Riddler is devising yet another trap for Batman to ...
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5answers
2k views

Bizarre Love Triangle

I work in quite an unusual office. Everybody who works here has a colour for their surname! It’s a bit like that old board game Cluedo, except nobody has been murdered. Still, there is a bit of a ...
16
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1answer
694 views

Complete the world's longest self-documenting sentence

Complete the following by filling in the blanks with written numbers to create the world's longest self-documenting sentence. ...
16
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3answers
2k views

3 gates and a drop of acid

I was playing with some electronics recently, and I had bought three logic gates to make a small flat device that took two inputs, I1 and I2, and returned them in the opposite order (I2 then I1). ...
16
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7answers
4k views

Five Men and Four Coins Puzzle

This is a puzzle of five men guessing how many stars will appear from tossing four coins. There are five men: Mr. Zero, Mr. One, Mr. Two, Mr. Three, and Mr. Four; playing with four coins. For each ...
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2answers
2k views

Houdini versus the chess masters

As we all know, Houdini is very good at coming out on top against improbable odds! And oh boy are the odds improbable. For his next great performance, he claims he can play simultaneous chess games ...
16
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1answer
2k views

Finally, you wake up from a coma

You can barely open your eyes when a doctor walks up to you: You are a lucky one. Not many people have survived an accident like this. Only a handful of neurosurgeons are able to perform such an ...
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3answers
2k views

Star Puzzle: Determine which circles are True and which circles are False

A circle with number x means: “This circle is connected (straight line) to x circles with a true statement” This is valid only if the statement in the circle is True. If a circle is False, ...
16
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5answers
871 views

4 Gridded Prime Numbers

You have the first four prime numbers ($2$,$3$,$5$ and $7$) which are gridded and shown as below: You are trying to get highest total score you can reach with arranging the numbers by rotating (no ...
16
votes
1answer
499 views

Statue Park: Knight's Lines

This is a Statue Park puzzle. Rules of Statue Park: Shade some cells of the grid to form the given set of pieces. Pieces may be rotated or reflected. Pieces cannot be orthogonally adjacent (though ...
16
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2answers
2k views

What are the three numbers in this puzzle?

There are three people in a room without any equipment. Each one has a number on his forehead Every person knows the numbers the other two have, Every person knows that his number is either the sum ...
16
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3answers
2k views

Lies, damned lies, and statistics

A (hopefully) new variant on the Knights & Knaves problem. On the island of D'Israel, the inhabitants fall into three types: Liars, Damned Liars, and Statisticians. They are visually ...