Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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).

15
votes
5answers
1k views

30 fake coins out of 99 coins

You are given 99 coins which consists of 30 fake ones. You also have a digital balance scale with perfect precision that shows how much difference between weighs you put on. For example, if you put 10 ...
12
votes
11answers
4k views

Coin Game with infinite paradox

Here’s the puzzle/problem: Let’s presume we are best friends. I own the house next to you. I make a gaming proposition along the following lines: You throw a coin over and over again. So long as it ...
-2
votes
1answer
475 views

Don't be Greedy

this is a cs50 puzzle day 2019 question as you would know the questions have a one english word answer. will someone like to collab with me to solve all of them? there are 10 more of them.
1
vote
2answers
146 views

Sequence made of symbols

(My friend in real life gave me this)That's the original sequence: ⬅↕➡,⬅↕,➡,⬅,?,?,↕➡ I'm going to use other symbols to make it readable: (/), (/,), (/, ?, ?, /) I've noticed that the comma ...
11
votes
1answer
559 views

Reflections in a Square

An ideal billiards table (no friction, ideal reflections off of the walls, no pockets) is shaped like a square. From the bottom-left corner, shoot a point-sized cue ball at some angle. What is the ...
4
votes
5answers
2k views

Find 108 by using 3,4,6

Assemble a formula using the numbers $3$, $4$ and $6$ in any order to make 108. You may use the operations; $x + y$ $x - y$ $x \times y$ $x \div y$ $x!$ $\sqrt{x}$ $\sqrt[\leftroot{-2}\uproot{2}x]{...
40
votes
11answers
8k views

3 doors, three guards, one stone

You are in a room with three doors. You find out that behind two of these doors, the darkest pit of hell is waiting for you to make a mistake. The other door leads to heaven, where you obviously want ...
-5
votes
0answers
82 views

Help me solve this riddle, please [closed]

There once was a man with seven sons. One of his sons was very smart. Four of his sons are of average intelligence. The four sons that were of average intelligence but much smarter than the one. But ...
9
votes
1answer
533 views

Girl Hackers - Logic Puzzle

StackExchange Top Ranked Girl Hackers The Stack Exchange Hacking Federation (of course fictitious) has just released its list of top-ranked female hackers for the year. Using only the clues below, ...
10
votes
5answers
2k views

Sum letters are not two different

The following letters all have something in common which may not be obvious at a first glance: A B D H P No other letters share this attribute. Hint More ...
3
votes
5answers
328 views

A story about liars

Evelyn, Skylar, Alayna, Madelyn, Jonathon, Lara, Alyin, Felix, Iris, Bob and Roslina live on an island where some people always tell the truth, and the rest always lie. Roslina says "Alyin and Evelyn ...
18
votes
2answers
57k views

A man with two red pills and two white pills

Story: A Color blind man is travelling in a somewhat famous ship that had just a few people on board. Everything was smooth sailing for some days. One day,the man heard some noises from outside when ...
10
votes
2answers
1k views

8 Prisoners wearing hats

A warden lines up these prisoners. He announces, "I see a white hat." He then leaves the room. Every few minutes he comes back in and asks if anybody knows their hat color. Anyone who figured it out ...
20
votes
12answers
114k views

Four prisoners wearing black and white hats

There are four prisoners. All four prisoners will be freed, if at least one of them correctly guesses the color of the hat on his head. They can't speak to each other, and they can't touch each other....
27
votes
12answers
2k views
9
votes
3answers
2k views

Science Themed Logic Problem

I have this question as extra credit for my chemistry class. Im passed the deadline for EC so i don't even care about that, the answer is just driving me crazy! No one else has figured it out that i ...
5
votes
3answers
282 views

Can't figure this one out.. What is the missing box?

I've been stuck on this for ages, and can't figure this out. What is the missing box, and the logic behind the answer? This was taken from a Korn Ferry Leadership Assessment practice trial.
15
votes
2answers
571 views

What is the Universal Translator censoring?

Lieutenant, launch the polar probes! Launching probes, sir. Failure, sir. Probes did not land at the poles. Well!? Where are they? Unknown, sir. Somewhere off-axis. They did land on ...
36
votes
5answers
10k views

Sabotage at Sea - Cursed Cruise liner?

(Warning: Heavy reading incoming. I suggest writing stuff down...) It's now the year 2150, and you're one of the few people who didn't leave earth twenty years ago. Why? A deadly disease overtook the ...
2
votes
1answer
142 views

Pattern Recognition: $7 \star 8$ =?

The following pattern was given to me by one of my friends: If $$\quad 5 \star 5 = 10$$ $$\quad 6 \star 6=18$$ $$\quad 7 \star 7=36$$ then $$\quad 7 \star 8 = ?$$ a) $54 \quad$ b) $51 \...
3
votes
12answers
2k views

English Logic Puzzle [closed]

On this site, I found this: "If some Smaugs are Thors and some Thors are Thrains, then some Smaugs are definitely Thrains." Options: TRUE, FALSE, NEITHER The answer given is FALSE. However, I ...
6
votes
1answer
407 views

Games and Puzzles

Four teams take part in a week-long tournament in which every team plays every other team twice, and each team plays one game per day. The diagram below on the left shows the final scoreboard, part of ...
9
votes
2answers
295 views

Bold, vivid family

I remember organising the colours of the rainbow in columns. In the way that I did, I could create the word RAINBOW from certain letters in each word, indicated by the columns they were each placed in....
6
votes
1answer
588 views

Bongard n°4: Neutral vs Town

This is my last puzzle before the holidays, have a nice summer everyone. Here's a link to the rules of these kind of problems: There are six boxes on the left, and another six on the right. The ...
6
votes
5answers
949 views

20 cards facing down

You have a row of $20$ cards facing down. A 'move' consists of the following actions performed in sequence: Pick a face-down card and flip it face-up If there is one, also flip the next card on ...
9
votes
4answers
1k views

JonMark Perry's Grid Logic Puzzle

Consider the following puzzle type proposed by JonMark Perry. Start with a square grid of arrows, each one pointing in one of the four cardinal directions. For example: You start at the ...
8
votes
4answers
721 views

A simple murder mystery puzzle that I came up with

A woman was found dead in her apartment. She was hanging from the ceiling but the detectives deduced that it was not suicide because of the bruises on her body (indicating a struggle) and the mess in ...
3
votes
1answer
774 views

Which of the six tiles is missing? — An IQ Test Question

Which of the six tiles below is missing? I honestly do not know the answer. I took a screenshot of this from an online IQ test a while back. If you know where it is from, please let me know, and I ...
-1
votes
0answers
55 views

What is the solution for this progression puzzle? [duplicate]

I encountered this in an online test and was unable to solve it. My approach was that the sticks were rotating, like hands of a clock in either direction at different rates. But by using this I was ...
4
votes
2answers
272 views

Gold, silver and bronze in the balance

Equivalent to finding three heaviest coins in order of weight, on a balance that holds one coin on each side. (Simplified, with some Wikipedia references corrected, from the original puzzle. The ...
4
votes
4answers
156 views

What is the minimum High Card Points needed for a partnership to be able to claim all 13 tricks in Bridge?

Assume you have basic knowledge of how a contract bridge game plays. There are 40 total HCPs in a set of cards. 4 for each Ace, 3 for each King, 2 for each Queen and 1 for each Jack. What is the ...
19
votes
1answer
730 views

Logic puzzle: Driving around the United States

For Super Bowl Sunday, here's a super-sized logic puzzle! This was a practice puzzle for a hunt I participated in a few years ago. There are ten delivery drivers driving around the United States of ...
-3
votes
0answers
180 views

IQ test question from Vietnam [duplicate]

If anyone know how to do it? Confuse from https://testiq.vn/iq-test.html
0
votes
2answers
8k views

Which number should replace the question mark?

There is a picture. Find out what number is needed to replace this question mark.
5
votes
3answers
259 views

What's the hand of the lonely man?

Albert, Fred, Larry, Ron and Patrick are playing cards at Albert’s house with a regular 52 card deck that is missing all the 2s. Patrick has 10 cards, none of which are higher than 6. Ron has 13 cards,...
7
votes
1answer
178 views

Pattern Recognition problem : $… ,224,8,3,4,11,…$

The following pattern was given to me by one of my friend: $$\color{red}{224}$$ $$14 \quad \quad 8$$ $$4 \quad \quad \quad \quad \quad 3$$ $$8 \quad \quad \quad \quad \quad \quad \quad 4$$ $...
21
votes
8answers
2k views

Which one is the true statement? [closed]

All five statements below are true. None of the four statements below are true. Both of the statements above are true. Exactly one of the three statements above is true. None of the four statements ...
34
votes
3answers
5k views

Do better than chance

You and an opponent are playing the following game: Your opponent picks two different real numbers, however he wants to, and writes them on two cards, which he presents to you face down You choose ...
7
votes
3answers
381 views

Writing differences on a blackboard

The numbers 25 and 36 are written on a blackboard. At each turn, a player writes on the blackboard the (positive) difference between two numbers already on the blackboard, if this number does not ...
5
votes
5answers
639 views

The Pebbles Quiz

We are in a TV game. We have 8 same looking boxes, each of which has 2 pebbles. Each pebble could be either precious or not precious. We choose a box and the host, without looking inside the box, ...
1
vote
3answers
2k views

Matrix type IQ puzzle [closed]

Found these tasks, although not looking too advanced, I can't seem to solve them. What are the solutions and why? Task 1 Task 2
8
votes
2answers
252 views

Masyu puzzles with many circles

The rules of Masyu: Make a single loop with lines passing through the centers of cells, horizontally or vertically. The loop never crosses itself, branches off, or goes through the same cell ...
-4
votes
0answers
82 views

Which gate leads to heaven? [duplicate]

You are standing before two doors. One of the path leads to heaven and the other one leads to hell. There are two guardians, one by each door. You know one of them always tells the truth and the other ...
48
votes
15answers
6k views

Find the identity of the four troll brothers

The four troll brothers Wudhor, Xhaqan, Yijlob and Zrowag have the following properties: Wudhor always says the truth. Xhaqan always lies. Yijlob lies or says the truth unpredictably. ...
7
votes
4answers
302 views

Best way to pay for college puzzle

In a society, everyone goes to college and everyone has 3 children(one parent family). College is also very expensive. There are two ways that this society could pay for college. Let's say college ...
14
votes
1answer
410 views

Keeping a ball lost forever

Suppose you can make a rectangular maze, where each cell (apart from the bottom-right) can contain an arrow in one of the four directions (up, down, left or right) of your choosing, except for those ...
86
votes
15answers
842k views

Two doors with two guards - one lies, one tells the truth

You are a prisoner in a room with 2 doors and 2 guards. One of the doors will guide you to freedom and behind the other is a hangman --you don't know which is which. One of the guards always tells ...
10
votes
3answers
11k views

Knights , Knaves and Spies - Part 1

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 ...
7
votes
5answers
659 views

Highest possible score my friend could earn in one Scrabble turn?

My friend has a great vocabulary but is also quote humble. Every time we play Scrabble he wins easily. He says he tries his best, with one exception: If the opportunity ever arose, he would never ...
7
votes
1answer
306 views

Fair way to split coins [duplicate]

Alice and Bob went walking in the desert. Alice had two gallons of water and Bob had three gallons. They met Charlie who had no water at all and they all (Alice, Bob, and Charlie) shared the five ...