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).

-8
votes
6answers
688 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
746 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
469 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
940 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 ...
24
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
830 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
2k 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 ...
5
votes
4answers
3k views

Are you Really Smart

The government has introduced a standardised test to identify dumb people and make them ineligible to apply for any government jobs, a pass in the exam is mandatory for applications in future. It ...
7
votes
2answers
2k views

Can you help the traveller

A traveller decided to explore a square desert. He started from a point on the edge to point B, travelling perpendicular to the edge of the desert he started on. On reaching B, he then decided to take ...
-3
votes
1answer
329 views

Apples and Oranges

You were on a grocery shopping day, you go to the store, and your friend tells you he'd like you to pick him up some fruit, naturally you try and be a kind friend and agrees to pick it up for him, you ...
2
votes
3answers
701 views

4 Doors and a Half Value prize

You're on a game show, playing for 1 million dollars! You've made it to the final round, there are 4 doors, you pick a random door (obviously, there's a 1/4 chance for all of them, let's say you ...
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 ...
7
votes
4answers
1k 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, ...
3
votes
2answers
587 views

When will the matrix turn to black?

For the following pattern of filling the $5*5$ matrix, how many steps does it take to turn all cells of the matrix to black? Pattern has revealed by eBusiness: I guess after some steps next pointed ...
1
vote
1answer
548 views

How do I count Hamiltonian paths of grid?

Let's say there is a 5x5 grid with a starting position in the upper left corner, and an ending position is lower left corner. How do I count how many Hamiltonian paths there are through the grid? I ...
5
votes
1answer
715 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!
6
votes
2answers
1k views

Percentages and the watermelon size reduction

Ok, so my friends and I had a disagreement over this seemingly simple problem and we would very much like to know the answer for it. Question Initially a 100 kgs watermelon is 96pc water and ...
4
votes
2answers
996 views

How Many Queens to Threat Themselves?

How many queens can be placed in a standard $8*8$ chessboard to threat each of them exactly once by other queens?
4
votes
1answer
770 views

The knaves come out at night

Standard knights and knaves problem. There are 10 people in a room, you know that each person will either always tell the truth or always lie, but you don't know who is a truth teller or liar. You ...
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, ...
1
vote
3answers
2k views

A square and a circle at once [closed]

Can you draw something on a piece of paper that looks like a square and a circle at the same time? ( without using Math or 3-d visualisation techniques)
3
votes
2answers
3k views

Men digging holes

Suppose 9 men take 9 hours to dig 9 holes in the ground. (a) How many hours would it take 3 men to dig 3 holes? (b) How many men would it take to dig 54 holes in 54 hours?
2
votes
1answer
272 views

The Moving Bots

Each of the 50 robots move around in a room. The room is 8 by 8 tiles long. Each bot takes up 1 tile. On each turn they move like the knight in Chess, they don't teleport, they move. They all move at ...
0
votes
1answer
1k views

Clue for the Treasure Hunter

One day a treasure hunter was searching for treasure on an abandoned island. He got tired of looking everywhere, so he walked towards a big tree that he saw in order to rest in its shade. As he ...
5
votes
1answer
353 views

Val, Lynn Chris

This is taken from a riddle book: Val, Lynn and Chris are related to each other, but no incestuously. Among the three are Val's father, Lynn's only daughter, and Chris' sibling. Chris' sibling is ...
7
votes
3answers
755 views

Searching for gold

You are a treasure hunter in search of the legendary gold of the Isle of Goon. According to your research the gold is buried either behind the old church, or under the giant palm tree. You travel to ...
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 ...
3
votes
1answer
251 views

Non-Diagonal Pointing Problem

You can see the rules for pointing problem at this article. It has been clarified that there is no solution to this question. But, what if we remove the diagonal rule? is there any solution?
8
votes
2answers
550 views

How to let all people in Group A talk to all people in Group B in a shortest amount of time?

Ok, let say Group A has N number of people, and Group B has M number of people. I want each person in Group A to have a fixed T time conversation ( time T is fixed like 5 min or 10 min) with each ...
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,...
7
votes
1answer
558 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). ...
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 ...
11
votes
2answers
696 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. ...
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 ...
7
votes
1answer
492 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
640 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 ...
1
vote
1answer
549 views

Could a gold/{second metal} crown the be created that would pass the Archimedes test cost effectively? [closed]

Many people are familiar with the story of Archimedes submerging a crown in water to identify if the volume of the crown was consistent with the volume of the same amount of gold. The test was to see ...
5
votes
1answer
796 views

Clock Puzzle problem

Today I came across this puzzle: How many minutes is it until six o'clock if fifty minutes ago it was four times as many minutes past three o'clock? Any help?