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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3
votes
2answers
433 views

find the order of fruits

There are five fruits (Apple, Banana, Pineapple, Orange and Watermelon) that should be ordered in their places. But we do not have enough containers for them: there are only two bowls and two baskets. ...
-8
votes
6answers
719 views

Three Wise Monkeys and a Crime [closed]

Is there any crime the three wise monkeys (who see no evil, hear no evil, and speak no evil) could collectively "witness" and not be able to indict the suspect?
11
votes
2answers
9k views

Divide a rectangle with a rectangular hole into two equal parts

Consider any large rectangle from which a smaller rectangular portion has been removed. The removed rectangular portion may have any orientation i.e. the remaining figure is not necessarily symmetric ...
9
votes
2answers
1k views

Entangled physicists

The anti-intellectuals have won the war, and under the iron rule of emperor Nonotin anyone who has been deemed too smart for their own good has been brought to labour camps. But most of the science ...
1
vote
2answers
1k views

Find the order of students presentation(logical puzzle)

Four students P, Q, R and S each working under the super vision of one of the four professors A, B, C and D made their final year MBA Project Presentations one by one, one each in the areas of Finance,...
5
votes
1answer
733 views

Find the pattern of matrices

fill the matrix correctly and the guess the Letter and number of 5th matrix: PS: I'm sure you won't need options!
14
votes
3answers
2k views

The defective clock

James has a defective clock in his room. The clock is digital, and some of the seven bars on its units digit are broken. A bar that works is on when it should be and off when it should be, whereas a ...
9
votes
2answers
3k views

Color the Table

Color each cell of the table with following rules: Yellow and Orange cells are adjacent, but Red and Black are not. Cell with number 3 is White, Green, Blue or Red and the cell with number 5 is not ...
7
votes
3answers
30k views

Split 12 liters in half with 5 and 8 liter bottles [duplicate]

You have 12 liters of apple juice in a 12 liters bucket and you want to share it with your best friend. But you have an empty 8-liter and an empty 5-liter bottle. How do you split the apple juice in ...
13
votes
1answer
3k views

The seven piece silver chain

You have to stay for 7 days in a hotel outside your city. But you forgot to bring your credit card and are out of cash. You have a silver chain with 7 links. The rule in this hotel is that residents ...
92
votes
16answers
920k views

Two doors with two guards - one lies, one tells the truth

You are a prisoner in a room with 2 doors and 2 guards. One of the doors will guide you to freedom and behind the other is a hangman --you don't know which is which. One of the guards always tells ...
4
votes
1answer
577 views

Which one is the lightest marble?

There are 8 marbles that one of them is lighter than the others, and all other seven marbles have the same weight. There is a balance scale that you can use it twice or once. Is there any way to find ...
-2
votes
1answer
711 views

Find the Different Sugar Cubes [duplicate]

There are 10 Boxes, each contains 1000 sugar cubes. The sugar cubes in 9 of the boxes are 10 grams each and the other box has 9 gram cubes. There is a digital scale that you can use it ONCE. (i.e. ...
7
votes
1answer
561 views

A cube puzzle (Multiple of 6)

If you have a cube, say, $3 \times 3 \times 3$, you know that mathematically it's made of $27$ ($3*3*3$) smaller cubes. Now, just remove one full line of smaller cubes (in this case, 3 smaller cubes). ...
3
votes
2answers
1k views

Unknown Consecutive Integers Puzzle

Two people, Anne and Bob, each hold an index card. A positive integer is printed on each index card, and these integers are consecutive (i.e. Anne's card may display 8 and Bob's card 7). Anne and Bob ...
22
votes
4answers
3k views

The Monty Hall problem

I'm amazed that, although well known, this problem hasn't been posted yet. Monty Hall You are on a game show. The host of the show shows you three doors. He tells you that behind one of them, is a ...
7
votes
4answers
2k views

Three 50/50 guesses

Three friends enter a quiz-show as a team, the final round of the show is all or nothing, they only get their prize if they can win this round. Three boxes labelled 1, 2 and 3 are placed in a room, ...
20
votes
3answers
6k views

The lake monster

You are on a rowboat in the middle of a large, perfectly circular lake. On the perimeter of the lake is a monster who wants to eat you, but fortunately, he can't swim. He can run (along the perimeter)...
15
votes
1answer
2k views

Is this a new kind of liar puzzle?

I would like to ask if anyone has seen elsewhere this variation on the standard truth tellers/liars kind of puzzle. In the usual repertoire it is assumed that every person questioned knows the answer ...
0
votes
1answer
7k views

10 little dwarves [duplicate]

A dwarf-killing giant lines up 10 dwarfs from shortest to tallest. Each dwarf can see all the shortest dwarfs in front of him, but cannot see the dwarfs behind himself. The giant randomly puts a ...
5
votes
1answer
1k views

Put numbers from 1 to 6 in the puzzle

Put the numbers from 1 to 6 in the puzzle in a way such that: In each row or column there shouldn't are no duplicate numbers. The squares that are joined together have the same number.
11
votes
2answers
698 views

First number, which can not be defined

What is the appropriate answer to this question? What is the first natural number, which can not be defined with less than 15 words? Explanations: 1. Natural means integers greater than 0. ...
27
votes
5answers
4k views

First odd number in a “number dictionary”

All numbers between 1 and 1010 are written out and ordered alphabetically into a dictionary (as the only entries). Spaces and hyphens are removed. 1024 would then be "onethousandtwentyfour". Also, "...
21
votes
12answers
126k views

Four prisoners wearing black and white hats

There are four prisoners. All four prisoners will be freed, if at least one of them correctly guesses the color of the hat on his head. They can't speak to each other, and they can't touch each other....
20
votes
2answers
10k views

Coin weighing problem

You are given ten stacks of golden coins, each stack consisting of ten coins and a digital scale with arbitrary precision. You know that all stacks of coins are made from gold, weighing 10 grams per ...
7
votes
4answers
379k views

Puzzle of putting numbers 1-9 in 3x3 Grid to add up to 15

In a 3x3 grid, I'd have to put numbers from 1 to 9 in a manner so that respective row, column and diagonal add up to 15. I have only been able to come up with one solution: $$\begin{array}{ccc} 6 &...
7
votes
1answer
509 views

Number of true sentences

You are given a sheet of paper with $100$ sentences, in the form of: There are exactly $x$ wrong sentences on this sheet. There is exactly $1$ wrong sentence on this sheet. There are exactly $...
1
vote
1answer
646 views

3 Switches identification [duplicate]

Picture this. You are in a hallway of a very large office building. Near you are 50 light switches of which 3 are unlabled. These lightswitches are connected to 3 lights in 3 separate rooms. The ...
2
votes
10answers
5k views

The cage - a logic puzzle

One summer day John was jogging in the countryside wearing only his normal running clothes (shorts, vest, sports shoes and socks). After running for some time he saw that the lace of one of sports ...
7
votes
2answers
4k views

Spatial IQ test puzzles

The following puzzles were created by Robert Lato to measure IQ in range between 160 and 190. Whats the solution to them? You are supposed to draw in the dented boxes what the missing figure is ...
8
votes
2answers
621 views

Middle weight puzzle

There are 100 white and 101 black balls. All the balls have different weights. Balls of the same colour look the same. White balls are numbered from lighter to heavier (from 1 to 100). The same is ...
11
votes
6answers
6k views

Who has mud on their forehead?

This is probably my favorite puzzle. It uses logic, but it's not one of those "logic table" puzzles which i dislike immensely. What is this type of puzzle called and are there more like it that are ...
25
votes
5answers
3k views

How much red sand and how much blue sand?

This is a puzzle I remember arguing with my sister about when we were little... (Not quite as loud (or as public!) as the Monty Hall argument we had.) You have two large beakers of the same size. ...
14
votes
5answers
2k views

Church charity lottery

Suppose you've rigged the church charity lottery so that you cannot lose (what a swell guy you are). There are 10 drawings, and you start off with 10 dollars exactly. At each drawing, you must chose ...
5
votes
2answers
2k views

I have a pattern problem to solve!

The question reads: From the given pattern, What comes in place of '?'
7
votes
3answers
1k views

How do I solve the “Between Worlds” Android puzzle game?

I've been struggling for a while with the Between Worlds Android game, and have not yet solved it. I've only noticed a couple vague properties that hold in localized cases. To operate the puzzle, ...
8
votes
1answer
858 views

Number of tries to guess M-1 letters from M-letters-code

There are $N$ letters in an alphabet. There is a combination lock, the code to it consists from $M$ different letters. You can input $M$ letters combination and try to open the lock. (But you can't ...
8
votes
4answers
1k views

How to lock a shared artefact

This answer reminded me of a nice puzzle. I present it as a challenge for you. N thieves had stolen a magical artefact. They bought a lock with N keys and attached the artefact to a loop on a wall ...
17
votes
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?
11
votes
1answer
3k views

How to solve this crazy Chinese puzzle for children?

I have been shown this "Chinese puzzle from textbook for 2nd grade" like a joke. But it is intriguing, so I would like to know the answer, but I am quite bad in associative puzzles and can't find the ...
16
votes
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?
11
votes
8answers
11k views

Survive from death by asking the right question from trolls

You are in the intersection of two roads, there is a troll in the beginning of each road. One of them is liar (always lies), and one of them always tells the truth. One of the roads, ends to your ...
3
votes
2answers
666 views

How to generalise Partition of the pie for N envy people?

There is well known task: How to divide a pie between two people, so each will think that he got equal or more that the other one? It has the following solution: I know that it is possible to ...
30
votes
5answers
6k views

Two spies throwing stones into a river

There is a puzzle about two spies: Two spies must pass each other two secret numbers (one number per spy), unnoticed by their enemies. They have agreed on a method for doing this using only 26 ...
18
votes
3answers
3k views

Knights and jokers

There are $N$ men. $K$ of them are knights, $M$ of them are jokers. $N$ is known, $K$ and $M$ are unknown. You know that: $K + M = N$, $K \gt M$, $M \ge 1$, $N$ is odd. Knights always tell ...
19
votes
2answers
2k views

How to create a pure mathematical-logical based puzzle equivalent to resistance based physical puzzle?

I am thinking how to reformulate a physical puzzle in a way that it becomes purely logic based (doesn't uses physical lows and can be solved by a person, who knows nothing about physics). The puzzle: ...
25
votes
4answers
8k views

How do you solve a word puzzle when you have no idea where to start?

When you're looking at a logical word puzzle, what sorts of clues should you try to look for to solve them? There have been quite a few puzzles posted to this site so far that I spent a few minutes ...
21
votes
3answers
3k views

Winning an unfair game

I came across the following interesting problem today: A game consists of a sequence of plays; on each play either you or your opponent scores a point, you with probability $p < \frac{1}{2}$, he ...
16
votes
1answer
2k views

You are a cat. How do you swap?

Number twenty-one cages containing mice, 1, 2, 3, etc., up to 21, and place them in the following order: 1 14 15 17 3 7 13 6 20 2 19 21 5 18 8 11 16 9 12 4 10 ...
23
votes
4answers
7k views

Variation of 100 prisoners light problem

There is a classic problem below for which Dr. Yisong Song wrote a very well written and thought out series of solutions. The variation here I've never seen anywhere but am curious. I want to work it ...