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
763 views

The Three Seers

Your kingdom has been aided, for as long as anyone remembers, by three great seers. These seers are all-knowing and will truthfully answer one question of any person that seeks them. This question ...
1
vote
4answers
504 views

Puzzle: Covert spy investigation

You are working for the CIA as a spy. One day you get a secret offer from the US president to spy on the CIA for him and to go and investigate the truth about a CIA covert operation which happened 10 ...
17
votes
1answer
2k views

The Pirates of Beal Isle - very long logic grid puzzle

Story Let me tell ye a tale: Somewhere northeast o' the Bahamas there be a tiny scrap o' rocks stickin' up out o' the sea known as Beal Island. It be a barren, rocky place, and no man ever called it ...
1
vote
4answers
437 views

Where is the 1$ [duplicate]

The owner of a ration store sells sugar sacks weighing 50Kg for \$50, but he gives a special discount to his neighbors, and sells it to them for \$45. One day the owner, whose name is Jack, left the ...
6
votes
5answers
2k views

The isolated kingdom

In a kingdom, the King did not allow any citizen to visit the world outside. Also only a person with a proper paperwork was allowed to enter or he was sent back. A wooden bridge was the only ...
25
votes
11answers
6k views

Kill the jokers! - Part 1

The famous and ruthless explorer Wyoming Wilbert reports in one of his books that he once visited an island inhabited by jokers and truth tellers. Truth tellers always tell the truth, whereas jokers ...
18
votes
4answers
2k views

Past, Present and Future

There are 3 gods, named Past, Present and Future, who all look identical. They sit in a throne room, with one in the middle, the others on the right and left. You are allowed to ask them a series of ...
1
vote
1answer
261 views

Minimum lines to reach all 4x3 dots

There are 12 dots in a 4x3 grid pattern. You may start at any one point. You must travel as long as you want in a fixed direction, then stop and turn. Again you travel straight till you turn. (Each ...
0
votes
0answers
144 views

How many cheating husbands? [duplicate]

There is a matriarchal town which believes that a prophetic stranger will tell the wives whether any of the husbands are cheating. The stranger will only say yes if there are any and no if there are ...
13
votes
1answer
1k views

Visiting the gym this month

Question Three men visit a gym on a regular basis - one every two days, one every three days, and the last one visits once every week (on the same day). In a particular month, one of the 3 men's ...
2
votes
2answers
1k views

Hardest sum sudoku ever! (as well as how to solve them)

This sum sudoku is probably the hardest puzzle I've ever encountered, and I have made very little progress (a few cells or so). I found it in a book by Reader's Digest. The solution is given, but ...
2
votes
2answers
2k views

Knights , Knaves and Spies - Part 2

I was working my way through some Knight and Knave Puzzles in Discrete Maths by Rosen, when I came across the following question: There are inhabitants of an island on which there are three kinds ...
6
votes
1answer
835 views

Sherlock Holmes is at a Party

Ten people are at a fancy party. The guest list includes Obama, Shaq, Captain Falcon, Jaxon, Walter White, Bob, Emma Watson, Plato, Sherlock Holmes and John Watson. Sherlock and Watson arrive late to ...
8
votes
4answers
958 views

Male and female spiders on an infinite web

It is known that spiders of the species L. Latrunculorum Cannibalis build immense (virtually unlimited) communities where members arrange in huge chessboard-like webs with black males and white ...
7
votes
2answers
1k views

Four people in a dark lift

This is an old puzzle and won't take long to be solved, but I think it's a useful addition to the site. In a hotel in France at the time of the German occupation, two men and two women are in a ...
3
votes
2answers
2k views

The gardener problem

I tried to solve this, but I am unsure about my solution. I'm posting it here to see if I got it right. It is listed as multiple choice, but I am unsure about the quality of the puzzle creator, so don'...
0
votes
1answer
604 views

Tractor problem [closed]

An old farmer was walking beside a tractor, which was driven by another farmer. The farmer driving the tractor was dragging a pipe behind him. The old farmer wants to figure out how long the pipe is. ...
-2
votes
1answer
404 views

Deduce the numbers (addition + subtraction)

Two mathematicians are passing an exam, where the examiner informs them that he has chosen two different numbers between 2 and 100, such that one is divisible by the other. The examiner then tells the ...
3
votes
1answer
347 views

Ultimate family dart game

A family of 3 - a father, mother and son - are practising on a dart board. It has 3 shapes - a triangle, a circle and a square - on it. Scoring is as follows: Intersection of all 3 shapes - 5 points ...
8
votes
2answers
3k views

Numbers in quadrants of a circle - help me solve it

I saw this puzzle and don't know how to solve it: The only pattern I saw is 3 + 8 = 11 , 2 + 9 = 11, 6 + 2 = 8 and 1 + 7 = 8 Are there other approaches I should consider?
9
votes
2answers
796 views

The voters in a round table

There are $n$ MPs seated around a circular table, prepared to cast their votes on a single yes-or-no question. The voting goes by rounds. Each voter raises his hand for 'yes' and keeps it down for '...
11
votes
7answers
16k views

Is the Glass Half Full with water?

You, a right cylinder glass of water, 3 buttons, instructions, and a large flat land that seems to go on forever, are the only things that exist in a universe. In this weird universe, the exact same ...
2
votes
1answer
390 views

What will be the price of the dog? [closed]

Two men had a certain number of camels, and sold those camels. The price of each camel was equal to the total number of camels they owned initially. They then bought a certain number of goats for that ...
-5
votes
3answers
294 views

Scrap puzzle to count how many

There are 250 scraps. For each 11 removed, one extra can be obtained. How much maximum is possible, if one cut by one unit? I have read this somewhere, and one guy gave the answer as 25, but I can't ...
4
votes
3answers
386 views

Find the empty plot of land

Each of 4 brothers (Yellow, Green, Brown, and Red) has 5 rectangular plots of land. Land plots are numbered 1 to 21 in the diagram below. One of the plots is empty (not owned by any of the brothers). ...
1
vote
1answer
435 views

Find the next numbers in series? [duplicate]

Can you determine the next numbers in the below sequence? Here is the series. You need to find the possible numbers in 7th line. Series starts with 1 and it is like this. 1 1 1 2 1 1 1 1 2 3 1 1 2 2 1 ...
26
votes
4answers
6k views

Double whammy murder case! What happened?

It's Friday the 13th, and you and a group of 7 friends from the "Survivor" club belonging to University LeMao (A, B, C, D, E, F, and G) go camping. You're all pretty good friends, and talk quite a ...
2
votes
3answers
230 views

Drawing squares

Anafenza and Zurgo are playing a game. They have a playing board of $23*92$ squares. The idea of the game is to put a square(of any size) onto the playing board. The one who can't put any more ...
7
votes
3answers
865 views

The Wizard's Gambit

An evil wizard has captured and thrown you into a dungeon. This is not a normal dungeon though. It's magical. Each room has an associated "level" and 9 doors. The first door can be used to go to ...
-3
votes
1answer
1k views

Working schedule (with explanation) [closed]

Alice, Bob, Chris, Dave, Eric, Fred and Laura used to work in a restaurant 6 days a week, from Tuesday to Sunday (Monday is a day off). Every one works at least for one day, and at least two people ...
17
votes
3answers
2k views

Lies, damned lies, and statistics

A (hopefully) new variant on the Knights & Knaves problem. On the island of D'Israel, the inhabitants fall into three types: Liars, Damned Liars, and Statisticians. They are visually ...
-1
votes
1answer
22k views

The 12 islander question [duplicate]

There is an island with 12 islanders. All of the islanders individually weigh exactly the same amount, except for one (either weigh more, or less than the other 11). How can you find which islander is ...
3
votes
5answers
638 views

The three inheritors

A wealthy person has passed away, naming three siblings as beneficiaries of the vast estate. Unfortunately, the will states that: My estate shall be divided evenly, such that no sibling shall feel ...
2
votes
1answer
1k views

How to divide the vibranium bar into 3 pieces? [duplicate]

You have a bar of vibranium and the Cap needs to use it (not used up or consumed) every day but he only needs 1/7th on the first day, 2/7th on the second day and so on for 7 days. You have a ...
-3
votes
2answers
427 views

When will the bacteria fill the test kit? [closed]

A test kit, is a gathering place for a colony of bacteria. This Colony, at 12 pm cell division has created a bacteria. Every minute, every bacteria is divided into two bacteria. 12: 43 (43 minutes ...
7
votes
1answer
458 views

Highest place possible for Jessica - heptathlon scoring

121 women are competing in the heptathlon in Olympic Games. If British track and field star Jessica Ennis finishes in 104th place in every event, what is the highest place she can finish in the ...
-9
votes
6answers
4k views

What are the numbers?

Three perfect mathematicians with extremely strong memories are taking an exam. The examiner tells each of them a certain piece of information about $x$ and $y$, which two positive integers between ...
5
votes
2answers
1k views

Book stacking brain teaser

I've been given a puzzle, and I just can't work out an answer. Can you help? I'd also like to know your thought process for solving, as this matters more than the correct answer. Does it belong to a ...
1
vote
2answers
413 views

How much does the bag actually weigh?

A grocer has a set of two-pan balance scales for weighing food. A customer weighs a bag of sugar on one of the pans, which registers at 45 pounds. Suspicious, she swaps the bag to the second pan of ...
-5
votes
2answers
373 views

A few (very) easy puzzles [closed]

There are 7 sisters in a house. First one is reading a book, second is cooking, third is playing chess, fourth is solving sudoku, fifth is doing the laundry, sixth is watering the flowers. Question: ...
7
votes
1answer
1k views

Password Out of Date

Bob works at a high security institution. One day Bob tried to log into his computer and his password was denied. Then remembered that, for security reasons, the passwords were reset every month. So ...
9
votes
2answers
863 views

Color-Coded Bridges

Use the given clues to solve the puzzle below. Note: an image editing tool is recommended.
46
votes
10answers
15k views

Puzzle: Who hacked the computer?

I was working my way through some Knight and Knave Puzzles in Discrete Maths by Rosen, when I came across the following question: Four friends have been identified as suspects for an unauthorized ...
3
votes
1answer
370 views

Finding a murderer from statements from suspects

Officer X was entrusted with the duty of investigating a murder. The dead body was found in the living room. Preliminary investigation suggested that four of the six suspects were liars (at least one ...
6
votes
2answers
434 views

The 169 members of the Dinner Club

The Dinner club has 169 members, and professor Erasmus is one of them. Every evening, four of the members meet and have dinner together in a fancy restaurant. Professor Erasmus claims that today is a ...
8
votes
2answers
743 views

In the space station

There is a space station which has several chambers and each chamber is connected with a tube. Five mathematicians A, B, C, D, and E were gathered in a lounge of the space station. Suddenly, E ...
-2
votes
2answers
199 views

Shifting the stack as it is

There are $3$ saucers. And there are $5$ disks, say A,B,C,D,E, having respective areas $1,2,3,4,5$. That is, E is the largest disk and A is the smallest one. They are placed in the order E,D,C,B,A in ...
6
votes
3answers
507 views

Paying for drinks with Mexican and Texan dollars

The story is told that when the Republic of Texas was feuding with Mexico, there was a law passed by Texas to the effect that a Mexican silver dollar was worth only 50 cents in Texas; whereupon Mexico ...
-4
votes
1answer
2k views

How can the man get across the river with the two animals and the cabbage? [duplicate]

A man has a wolf, a goat, and a cabbage. He must cross a river with the two animals and the cabbage. There is a small rowing boat, in which he can take only one thing with him at a time. If, however, ...
-2
votes
2answers
509 views

Binary manipulation game

I made a (for now, 2 player) game once that deals with manipulating binary numbers on a single list. Here are the rules. Rules For now, take $n=5$. If possible, provide a solution for generalized $n$...