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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9
votes
2answers
778 views

Variants to blue eyes puzzle

Here are some variants to the Blue Eyes puzzle. All the rules are the same, but there are differences in (a) the number of people of different eye colors and (b) the oracle's statement. It is not ...
-6
votes
3answers
406 views

Catch the liar(s)

Alice: "Bob is lying, so is Charlie!" Bob: "Charlie is lying, so is Alice!" Charlie: "Alice is lying, so is Bob!" Who is/are lying?
22
votes
2answers
4k views

The Dwarves' Test

One day, the chief of the dwarves decided he wanted to test his tribe. So that night, he told the dwarves that he would paint on each dwarf's back a dot colored either red or blue. Each dwarf will ...
15
votes
2answers
1k views

Town of liars and truth-tellers with eccentric mayor

There is a small town with a strange custom. Residents each own a single pebble, painted blue or red, which they always carry in their pockets. Those with blue pebbles always tell the truth, and those ...
36
votes
12answers
5k views

Find the liar in the library

I've just taken a CS exam, which had the following question 6 persons entered a library the day a book got stolen. Each of them entered the library once and only once, and stayed there for some time, ...
3
votes
1answer
5k views

Which is the door to heaven [duplicate]

After living a peaceful and calm life, you die a painless death. Your spirit starts ascending into heaven when suddenly you are approaching two doors. Both doors are completely identical and there is ...
7
votes
3answers
811 views

Five numbers at the points of a star

I have a calendar with daily puzzles, and I want to verify something, so here is today's puzzle. I answered it myself and have the "official" answer as well. Please be sure to clearly state your ...
4
votes
1answer
260 views

Colored Pills True MADNESS -V2-

This riddle includes a small tweak to part 1 This isn't a duplicate. This riddle has one less pill. Because of this, the answer already provided wouldn't work here. You have two bags of similar (...
4
votes
1answer
486 views

Colored Pills MADNESS

You have two bags of similar (weight, texture) solid pills. One bag contains red pills and the other contains green pills. There are 13 pills in one bag and 14 pills in the other. Today, tomorrow, and ...
25
votes
11answers
14k views

What is my four digit car number?

My car has a four digit number. Its last digit is double the first digit its middle two digits are the same its last two digits are double the first two digits What is my car's number? ...
3
votes
1answer
318 views

The Prisoner of Brenda

Ripped from The Prisoner of Brenda with apologies to Matt Groening, Ken Keeler et al. Professor Farnsworth: "There. This time I'm sure I've fixed the Mind-switcher." An invention in which two people (...
-1
votes
2answers
346 views

All poisoned but one

There are $n$ large bottles of wine, out of which $n-1$ have been poisoned.However, consuming a single bottle does no harm, it requires all $n-1$ bottles (or small samples of them) to be consumed by ...
3
votes
6answers
2k views

Who killed the king's son?

The king has recently learned that his son has been killed by a mystery person. Wanting to know who committed the murder, he started to ask the people that have been around his son recently. He asked ...
12
votes
1answer
870 views

Ernie and the Underground Network

I haven't seen Ernie for a few weeks - he's been on holiday in the People's Republic of Kzijekistan (PRK). But yesterday I got an e-mail and thought I would share it with you. It reads as follows: ...
0
votes
0answers
83 views

Cyborg death match: Make your move [duplicate]

Found this one in my son's puzzle book. You are a cyborg in a death match with two other cyborgs. All three of you have identical blasters, and one single shot from these blasters will destroy any of ...
9
votes
3answers
672 views

Seven treasure chests

Seven treasure chests, made of gold, silver, tin, steel, brass, pewter and lead, each contain coins of one of the seven metals. No two chests contain the same type of coin. The pewter chest does not ...
2
votes
1answer
455 views

Find the odd coin

You have 11 visually identical coins. One of them is marked genuine (and you know which one this is). Out of the remaining 10 coins, all but one of them are also genuine, but you don't know which ones....
21
votes
3answers
3k views

Ten Tricky Mathematicians

Somewhere on the Hyperbolic Plane, you encounter ten mathematicians. You know that some of them always tell the truth while the rest always lie. Each of them knows which of the others tell the truth ...
71
votes
13answers
15k views

Three logicians walk out of the bar

It is known that when logicians get drunk they may claim not to know the answer to a question when they should know it very well. After a night of heavy drinking at the bar, three logicians decide ...
5
votes
1answer
569 views

The Minotaur's Labyrinth

You are trapped in a chamber in the center of the Minotaur's Labyrinth. There are $\mathbf{N}$ tunnels, $\mathbf{m}$ of which lead to safety; the remaining tunnels only lead back to the chamber. Each ...
7
votes
1answer
252 views

Guess another's present 2: Generalised

What if in Guess another's present problem introduce more present's colours? Also i would reduce a number of men to number of colours. So the task basically the following: N clever men receive ...
7
votes
6answers
790 views

Guess another's present

100 clever men receive presents from the president. Each man gets either a red or blue present, and only knows the color of his own gift. Then each man must guess a colour of a gift of some man: he ...
-5
votes
1answer
313 views

What are the missing items of this number sequence? [closed]

1, 2, 5, 13, ?, ?, 1 Please give explanation.
-1
votes
1answer
14k views

Who is the murderer? - logic puzzle

Three men are arrested on charges of murder. They make the following statements. First suspect: I'm not guilty of murder. Second suspect: the third suspect is the murderer. Third suspect: the first ...
5
votes
4answers
1k views

Find the missing object

1. 2. 3. 4. 5. 6. ? 7. Find the missing object (No. 6) Note:The first one to post an object with the matching criteria will be the winner.
17
votes
2answers
3k 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. ...
-5
votes
2answers
317 views

Double the fun with two puzzles [closed]

Here are the two puzzles that I have heard a long ago from my friends. 1) You can touch it with your right hand, but not with your left hand. What is it? 2) 10x+4x = 2y Then, what is x and y? ...
8
votes
2answers
436 views

The Security To The party [Part 23]

A party is being held at a local mansion. The host is very rich and his success is because of one thing ~ his famous recipe for Spaghetti! The only guests that may attend are people the host knows ...
6
votes
1answer
362 views

Draw the item after decoding the instructions

Draw the missing item replacing the question mark
7
votes
1answer
415 views

Chess tournament problem

12 chess players took part in a tournament. Each played against each other exactly once. After the tournament every chess player did 12 lists of names. On the first list, the player only wrote his ...
8
votes
2answers
2k views

Is it Always Possible? Colour Flipping

There's a 4x4 square, where switches are either red or green. When you flip a switch, all the buttons on that row and column will change color. Is every starting position possible to complete? If not ...
4
votes
1answer
336 views

Who are the guilty parties? #3

You've barely got back from the isolated villa where your last case was, when you hear that you are needed again: There is a group of people on board a yacht. The wealthy owner and her spouse have ...
-3
votes
2answers
482 views

Guess the missing alphabet!

What is the missing alphabet in below sequence? M T W T _ _ S
-2
votes
2answers
235 views

What cannot stand outside a door? [closed]

Let there be a house of which there is a beautified front door that is closed. Now: what is that "thing" for which it is impossible, logically (and irrefutably), to be outside this closed door?
20
votes
8answers
11k views

Logic puzzle - 3 suspects

An inspector knows that exactly one of 3 suspects committed a crime, and interviews them to find out which. Each person lies one time, and tells the truth the other time. A says: I did not do it. B ...
5
votes
1answer
371 views

Who Are The Guilty Parties? #2

You've barely got back from the island where your last case was, when you hear that you are needed again: There is a group of people at an isolated villa. In a curious twist, the aristocrats have ...
2
votes
1answer
557 views

Who are the guilty parties? #1

(Your investigations continue here.) I am testing this puzzle to see how it works, and gauge the difficulty. I have plans which will be unveiled in future puzzles of a similar nature, pending ...
20
votes
3answers
1k views

The mysterious card in the middle

The referee tells Lefty, Righty, and Middly: "I have picked three positive integers $L,M,R$ with $L<M<R$ and $L+M+R=13$, and I have written these numbers onto the three cards lying face down on ...
7
votes
1answer
684 views

The Beautiful Ladies' Brothers

The ladies mentioned in Five beautiful ladies have five brothers: Adam, Bob, Charlie, David, and Edward. Three have hazel eyes and are honest; two have lime-colored eyes and always lie. You are ...
1
vote
2answers
309 views

Simplest Magic Fruit Split with Magic Number [duplicate]

Anyone who plans to visit the Miracle Fruit Tree in the Royal Garden has to travel through Seven Gates in each of the Seven Curtain Walls surrounding the garden. Each of these gates has a guard. ...
-2
votes
1answer
3k views

Bus Driver's Age? [duplicate]

Imagine: You are a bus driver that drives from Delhi to Karachi and exactly 1987 kilometers. 1 liter fuel can end upto 105 kilometers . Every time driver stops at a fuel station he fills 3 liters of ...
1
vote
1answer
663 views

Find the missing value

find the value of 1 + 7 from the following. 3 + 3 = 3 5 + 4 = 4 1 + 0 = 3 2 + 3 = 4 3 + 4 = 5 1 + 7 = ?
0
votes
6answers
9k views

Missing number in a circle? [closed]

Here in this circle there are seven segments. 6 numbers have been written in 6 segments following a particular pattern. Find the number which will replace ??? in the seventh segment and also describe ...
7
votes
5answers
522 views

Ahmad, Ali, Amir and Nima in a tournament

Four players with first names Ahmad, Ali, Amir and Nima participated in a tournament. The highest ranked player defeated the other three, the second ranked player defeated the players in rank three ...
3
votes
2answers
6k views

Find the direction of the disc

You have a disc. One half of the disc is painted white and the other half is black. The disc rotates in either a clockwise direction or an anti-clockwise direction. There are two sensors which are ...
8
votes
10answers
3k views

A tiny question: The little big family

In a family, there are the following human members: Grandfather, grandmother, father, mother, son, daughter. All family members are inside a single room now. Question: What is the minimum amount of ...
5
votes
3answers
2k views

Crossword Puzzles: What is this crossword type?

I found these rules for a crossword, but I don't know what type it is. Can anyone help me? The rules: The words are given and you're asked to place them on the grid! The grid and the list of ...
11
votes
3answers
2k views

Creating a solved 9x9 Sudoku based on certain rules

The question: A rectangular fence is a set of 4 cells on a solved sudoku grid with co-ordinates $(i,j)$, $(m,j)$, $(m,n)$ and $(i,n)$. You can visualize this as the 4 corners of a rectangle. ...
12
votes
4answers
7k views

Who is the thief? An elementary school teacher had her purse stolen

Its not mine. I found it and didnt find it when i searched so i hope you guys enjoy. I did edit it somewhat. An elementary school teacher had her purse stolen. The thief had to be Sammy, Karin, ...
18
votes
6answers
4k views

Guess five binary digits!

Person A thinks of a 5 digit binary number. Person B tries to guess the number. B can guess a 5 digit binary number and A will respond with the number of correct digits (digits in the right place). ...

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