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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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14
votes
1answer
1k views

How to ensure your logic puzzle has no loopholes?

Alright, say you've made this logic based puzzle, but when you post it, people find tons of loop holes, that obviously wasn't what you want! You didn't tag it with lateral-thinking or brainteaser! It'...
18
votes
8answers
2k views

When should you rest?

You are in an airport and are worried about missing your flight. So you start to run the long distance to the flight gate at a steady speed of 10km/h (you have bags and are not very fit). ...
3
votes
2answers
2k views

whats the Missing Number?

In this grid of numbers, what is the missing number (in place of the question mark)? $$\begin{array}{|c|c|}\hline2&7\\\hline8&9\\\hline\end{array} \begin{array}{|c|c|}\hline0&3\\\hline5&...
4
votes
2answers
4k views

Puzzle : O' Barber , Who Art Thou?

I was working my way through some puzzles , when I came across the following question: An ancient Sicilian legend says that the barber in a remote town who can be reached only by traveling a ...
0
votes
0answers
104 views

A soft puzzle about a deaf ,dumb and a blind person [duplicate]

A deaf person stole a blind person's hen and a dumb person witnessed it.How can the dumb person convey this to the blind person?
18
votes
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 ...
21
votes
5answers
3k views

Knights and Knaves : Liar , Liar - How many are you?

There are 2014 persons in a row Each of them is either a Knave (who always lies) or a Knight (who always tells the truth). Each person says 'There are more knaves to my left than knights to my ...
7
votes
4answers
948 views

Can you help the robot cross the platforms?

You have created a robot with artificial intelligence, to test his abilities you add to the robot a battery pack which can hold a maximum of 5 charges and build for him an obstacle he needs to ...
7
votes
1answer
2k views

Caliban's Will puzzle

When Caliban's will was opened it was found to contain the following clause: I leave ten of my books to each of A, B, and C, who are to choose in a certain order. No person who has seen me in ...
9
votes
1answer
734 views

The Beverage Button

You stand before a panel with two buttons on it. One of them will dispense your favorite beverage, and you're dying for a sip. The other will destroy all life throughout the universe, so you'd ...
-7
votes
3answers
580 views

Cows eat too much [closed]

Cows are always hungry... 70 Cows eat all the plants on a pasture in 24 days. 30 Cows clear the same pasture in 60 days. How many cows are needed to clear the pasture by the end of 96th day?
4
votes
4answers
621 views

logic problem/puzzle solving

I'm here to ask you if it is possible to find a way to solve this problem. I'm designing the puzzle-enigma section of a video game and try to find possible solutions and mechanic for it. Imagine each ...
7
votes
4answers
2k views

Lying, truthful and merciless guards (variation)

This is a variation of the riddle of 2 guards and 2 doors: You are stuck in a room with 3 doors. Each of the doors have a guard posted. One guard always tells the truth, one always lies, and the ...
6
votes
5answers
1k views

A mouse, Two mousetraps, Eight houses

You are chasing a mouse living in a row of eight houses. Every night the mouse moves from the house it is in, to an adjacent house, and stays there the whole day. Apart from this, you have no a-priori ...
9
votes
1answer
1k views

The Old Millionaire

A very old man has a million dollars, which he's going to pass down to you! He has 3 associates who have been ordered to help you. The 3 associates know the location where it is, and they tell you it ...
11
votes
2answers
743 views

The Mysterious Disappearance of Doctor F. Andrews [Part 1]

This is my first real puzzle, so I hope you enjoy it! Sorry if the writing is a little poor, etc.. You are the unstoppable Detective Joshua Brown, and no puzzle can stand in your way! The Case: ...
9
votes
3answers
4k views

Is my sibling a sister [duplicate]

A male friend of yours wants to test if you are ok at Math and logical thinking, he says I am one of two children of my parents, and asks you to find out the probability that his sibling is a sister, ...
1
vote
0answers
2k views

The mad king and the 100 men who each have to guess the colour of their own hat [duplicate]

The following is the puzzle that I am trying to figure out. I know the "expected solution of 99". But honestly, I think this puzzle is flawed. How exactly can each wise man know the number of hats ...
4
votes
2answers
598 views

Left coin, Right coin, Last coin- A fair version

In this game, all players start sitting at a round table, each with a coin in their hand. At every turn, all players toss their coins together and put it on the table in front of them. Then each ...
6
votes
2answers
448 views

A model railroad story

Little Hans just got a model railroad kit from his grandfather for Christmas. His grandpa explained to him, that when he was young, he was a model railroad enthusiast, and encouraged his grandchild ...
4
votes
1answer
585 views

A Strange Sequence [duplicate]

This puzzle is taken from a French bestseller I read years ago. The solution is much simpler than it looks... Find the following line in this sequence : ...
4
votes
2answers
552 views

What's the sequence?

Joe likes 2025 but not 2024; he likes 529 but not 530; he likes 400 but not 500. Which does Joe like - 3600 or 3700? Why?
4
votes
3answers
970 views

A game of Green Jack

NB: This is based on a puzzle over at BrainBashers.com. The setup You and a friend play a card game called Green Jack. The deck consists of 16 cards, divided into 4 cards in 4 colors (standard ...
13
votes
1answer
920 views

Five professors and nine dishes

Here's yet another puzzle adapted from a puzzle book (in my case, with edits to make some of the specifications of the puzzle more clear because I didn't really understand them the first time I read ...
12
votes
2answers
3k views

Magic Squares in Sudoku Grids

A 3x3 magic square is a 3x3 grid containing the numbers 1-9 once each, and in which every row, column, and diagonal sums to 15: 294 753 618 And I presume we all ...
20
votes
1answer
2k views

The Illuminati and the Knights Templar

Some people in the American Senate are working for secret organizations. Some work for the Illuminati, some work for the Knights Templar, and some work for both. The are also innocent citizens who are ...
19
votes
1answer
5k views

Can you solve this logic puzzle in disguise? The color code behind the tomb

Another themed puzzle for you to enjoy. As with all my puzzles, please provided feedback about pro's and cons of the puzzle. The puzzle is self-contained (the link is just to provide a theme) and I ...
11
votes
4answers
2k views

Help me find my favourite DVD

I have an admission to make: I very rarely put my DVDs back in the case they came from. Whenever I watch a new DVD I just put whatever DVD is the player in the new case. I put the cases back on the ...
17
votes
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 ...
0
votes
3answers
3k views

Come out alive from locked room [duplicate]

You are locked in a 50 x 50 x 50-foot room which sits on 100-foot stilts. There is an open window at the coner of the room, near the floor, with a strong hook cemented into the floor by the window. So ...
5
votes
1answer
236 views

The strange exchange

You have two people in the center of an endless plane. Each one is holding some item that can fit in their palm, like a tennis ball. Both persons are identical in physical ability and brainpower. ...
3
votes
1answer
3k views

Who is the killer [closed]

A man was murdered in his office bathroom. Detective Troby found a paper with alphabets written as below from the pocket of the dead man's corpse. ...
9
votes
7answers
3k views

What is twice the answer to this question? [closed]

What is twice the answer to this question ? Just thought some people here would like this brain-teaser ;)
11
votes
10answers
5k views

The treasure hunt

An archaeologist who has just unearthed a long-sought-after pair of ancient treasure chests. One chest is plated with silver and the other is plated with gold. According to the legend one of the ...
6
votes
1answer
669 views

Find out which instruction is wrong

The object of the following flow-chart is to rearrange the numbers in boxes 1, 2 and 3 in such a fashion that, at the end: ...
2
votes
2answers
231 views

The hour glasses! [duplicate]

You have two hour glasses: A seven minute one and an 11 minute one. Using just these two hour glasses, accurately time 15 minutes.
-2
votes
1answer
398 views

The 'number of months' challenge [closed]

Okay, here I am having a puzzle for you all. The puzzle is quite short and clear in it's own way I am telling you. Rather than a question it's more like a challenge to you all (answer is already known)...
38
votes
1answer
4k views

So how did the date go?

It's Monday morning. Fernando just sat down at his desk for another hard day at work - programming stuff and answering telephone calls - "have you tried turning it off and on again?" As he is about ...
7
votes
2answers
2k views

Irreversible body swap

In Futurama's episode 6x10, the professor invents a device which allows to switch mind between two bodies. He then switches his mind with Amy. It later turns out that the a given pair of bodies can ...
14
votes
1answer
2k views

Knights and knaves in a foreign language

You die and ascend to heaven, there is a knight (truth-teller), a knave (pure liar) and a joker (random) sitting on a cloud - they all look the same. In order to gain entry you must determine their ...
9
votes
4answers
937 views

Generalized Path Guards

Suppose you are traveling and come to a fork in the road. One of them leads to something good like a cat shelter and a company handing out free ice cream and money, while the other leads to something ...
8
votes
3answers
1k views

The antisocial chair problem

A room has n empty chairs in a row. You choose a chair and sit it in it. Now someone else comes in and sits as far away as possible from everyone in the room or an arbitrary choice of furthest chair ...
3
votes
18answers
3k views

Why was the Five Star Hotel sued? [closed]

In a five star hotel, I ordered for a cup of coffee. When I was about to sip, I found a fly in the coffee. I complained. The manager apologized, took back the cup and brought another fresh hot one. ...
4
votes
2answers
715 views

Two Armies of Ants

I saw this puzzle a while back in a children's puzzle book, but I'll try to make it as accurate as possible. There is a small army of three ants walking down a very narrow road, so there is only ...
4
votes
2answers
543 views

Bob's expensive day

Bob leaves home with $50. His birthday approaching, he goes to the neighbourhood bakery to order a birthday cake and pays \$29.95 for the cake, plus \$3.08 for the candles. Then, he meets three ...
1
vote
0answers
7k views

An illness at a monastery [duplicate]

In Faraway Land there is a monastery built atop a mountain in which monks live isolated from the rest of the world. The monastery is made of two large buildings: one is where the monks sleep, the ...
6
votes
6answers
2k views

4 balls - red and blue

I have a black box that contains 4 balls. 3 are red and 1 is blue. I remove two from the box without seeing them. I look at one of them, it is red. What is the probability that the other one is ...
5
votes
3answers
646 views

I thought she liked me?

I'm a young programmer from NYC attending a conference in London. Last night I met a fellow developer in a bar she was young, beautiful and had the sexiest English accent! As the evening drew to a ...
-8
votes
6answers
726 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?
1
vote
4answers
748 views

What could have been the sentences I was thinking about?

I have just thought about an interesting problem in classical propositional logic to propose at this site, but lost my notes... I do recall, however, that the problem involved a particular contingent ...