# 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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### 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 ...
457 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....
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 ...
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 ...
573 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 ...
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 ...
791 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 ...
313 views

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

1, 2, 5, 13, ?, ?, 1 Please give explanation.
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 ...
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.
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. ...
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? ...
444 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 ...
363 views

### Draw the item after decoding the instructions

Draw the missing item replacing the question mark
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 ...
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 ...
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 ...
483 views

### Guess the missing alphabet!

What is the missing alphabet in below sequence? M T W T _ _ S
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?
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 ...
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 ...
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 ...
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 ...
688 views

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 ...
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. ...
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 ...
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 = ?
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 ...
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 ...
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 ...
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 ...
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 ...
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. ...
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, ...
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). ...
320 views

### Closing taps (generalisation) [closed]

You have a tanker that can hold any amount of water. You have $n$ taps that either let in or let out water. The rate of flow of water (in $ml/min$) for each tap is given by $f_n$ (positive for inflow, ...
755 views

### I Was Told It Would Explode

Story: There is a line of bombs, all over a building. You are the bomb defusal expert, and you are the one everyone is counting on the save the city, for as if any one of the bombs go off, you, and ...
256 views

### Colored stones on a chess board puzzle [closed]

We have a chess board of size n x n and there is exactly one stone on every square. We have green, blue and red stones. We must not have a row or a column full of stones of the same colour. We can ...
2k views

### Another village of liars and truth-tellers

There are two kinds of people living in a village: those who always lie (liars) and those who always tell the truth (truth-tellers). Everybody knows each other in the village and therefore knows ...
890 views

### The final showdown

I am amazed at my adviser's brilliance once again. Blackbeard's vanguard fleet was quickly sunk. And as luck would have it, the moment we finished cleaning up the mess, the scout returned with the ...
271 views

### The Hallway and Tele Doors ~ Prolong the Inevitable

Sequel to: The Hallway and Tele Doors Note: You need not have to read the above to understand this puzzle, however this puzzle does spoil the above one. The tele door system: Each pair of doors, ...
723 views

### mistakes in analogous puzzles from The Tipping Point

In the book 'The Tipping Point', Malcolm Gladwell cites two puzzles and draws an analogy between them, in fact he claims the two are equivalent. I believe there are some problems with both puzzles, ...
402 views

### End of piracy and beginning of technology

Blackbeard is no more, and everything seemed peaceful again, but during the last engagement with Blackbeard, my military adviser got introduced to the concept of "computer", and became very interested ...
623 views

### Find multiple dishonest people

Recently I travelled far distance by train and a stranger told me this riddle but I never got the answer: 100 years ago, when far distance travelling was something special, a traveller came back from ...
485 views

### Prepare for the counterattack

My adviser's brilliance crushed the Blackbeard's fleet, and we held a banquet to celebrate. The banquet was short lived however, for a arrow flew right past me and struck a pillar. Attached was a ...
586 views

### Dinosaurs and Elephants

There are two species living in the land of Puzzling: elephants and dinosaurs. Elephants always tell the truth when talking about an elephant, but always lie when talking about a dinosaur. ...
1k views

### Help with the name of this puzzle

When I was cleaning my basement I found one puzzle that my father gave me when I was a child. I really want to know the name of it! Could someone help me? The puzzle consist in 4 disks, and each ...
648 views

### Help locate enemy fleet

Few days ago, the notorious Blackbeard sunk 3 of my ships carrying exotic goods and treasures from Asia. I was furious and I am determined to send out my fleet to bring him to justice. However, as he ...
1k views

### The Hallway and Tele Doors

Assume you have an unlimited but finite number of linking, teleporting doors you can add to a hallway of finite length. Assuming there's a door at the start and finish, can you arrange the teleports ...