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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11
votes
2answers
745 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
608 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
450 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
982 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
924 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
239 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
670 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
399 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
942 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
722 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
544 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
648 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
736 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
751 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 ...
2
votes
3answers
4k views

Which sister to marry? [duplicate]

Tomorrow you will meet three sisters, and be married to one of them. The eldest always tells the truth, the youngest always lies. The middle sister lies or tells the truth at random. Knowing this, you ...
9
votes
5answers
1k views

Is the dog dead or alive?

Rocky the dog is alive. Rocky the dog is dead. Exactly one of statements 6 and 9 is true. Exactly one of statements 2 and 6 is false. Statements 4, 5 and 10 are all false. Exactly one of statements 1 ...
4
votes
3answers
904 views

The generous team puzzle

An intelligent team, ‘Smarty Pants’, applying to a competition completes an evaluation form early. Since they are feeling generous they randomly spread their assignment to all 10 teams applying from ...
8
votes
4answers
2k views

How do we get those dang Illuminati?

The Illuminati just stole our office They shot JFK and have committed numerous crimes against humanity (not really) but we usually let that slide. But for stealing our offices, we have decided to ...
2
votes
2answers
295 views

How many stamps?

Cade has six red stamps and three blue ones. In his collection, seven stamps are from Argentina and six stamps are from Sweden. One stamp is purple and it is not from Argentina or Sweden. Two of his ...
8
votes
3answers
2k views

A puzzle of trust and lies, allies and spies

Here is a puzzle involving distrust and asymmetric knowledge. (It was inspired by, but not exactly following, the board game The Resistance: Avalon.) There are ten resistance fighters trying to ...
8
votes
3answers
476 views

From Knights to Kings on a rectangle

In From knights to kings, we were asked On a NxN chess board $N^2$ knights are placed (one per cell). Each pair of knights, who control each other (i.e. one move away from each other) are friends. ...
2
votes
2answers
997 views

16 Buttons, Turn them all Red or Green?

There's 16 buttons arranged in a 4 by 4 square. They are coloured either red, or green. They appear like this (red being 1, green being 0) 1010 0101 1100 0011 Each press will switch all the ...
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 ...
4
votes
2answers
2k views

Banana? Or Orange?

25 kids were in a class, they were all trading lunches. Each kid traded their lunch 5 times. At first 12 kids had bananas. At first 13 kids had oranges 16 kids like bananas 14 kids like oranges In ...
8
votes
2answers
2k views

The way to Acarien puzzle

You are on a quest to the find the lost kingdom of Acarien. On your way, you end up at a fork in the road. Both paths look exactly the same. At the junction sits a wise man. The wise man will only ...
3
votes
2answers
840 views

Way to memorize shape - number combinations in short time [closed]

A visual memory test application gives some time to memorize images - numbers combinations, after that it shows a random shape and asks what the number is. What is to trick for such an application if ...
2
votes
1answer
5k views

Poisoned Bottle of Wine! [duplicate]

This puzzle is taken directly from a site and reworded. The site can be found at the bottom of this question. You are king of an empire and you are going to have a party soon. The party is the most ...
8
votes
1answer
3k views

Everybody loves my baby

James is in a room with three other people: Alice, Bob, and Spencer. Alice and Bob are married to each other, but James knows that Bob is secretly having an affair with Spencer. James is going to ...
2
votes
1answer
3k views

Water glass and wine glass [duplicate]

You have two equal glasses. One is filled with water. One is filled with wine. Now you take a spoonful from the water glass, put it into the wine glass, and stir until it is well mixed. Then you take ...