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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).

-2
votes
0answers
48 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 ...
47
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. ...
5
votes
4answers
210 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 ...
10
votes
1answer
337 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 ...
84
votes
15answers
829k 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
4answers
10k 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
626 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 ...
2
votes
3answers
1k views

Matrix type IQ puzzle

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
7
votes
1answer
282 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 ...
5
votes
1answer
167 views

Creatures from the Deep saw the heroes on a bridge

It was dark and cold in the land of Nemeria. A fellowship of heroes traversed a bridge in a straight line, one after another. Below them, only an abyss. They could hear the howling of strange ...
18
votes
1answer
2k views

What will the Frenchman say?

An Englishman, a Frenchman and a German are speaking. First the Englishman says : "M". Then the Frenchman says : "M" as well. And the German also says : "M". They all agree and decide to ...
11
votes
3answers
618 views

What's the combination for the safe?

The CFO sat back in his leather chair, which creaked and squeaked. "It's actually pleather," he said to the intern sitting nervously opposite him, a notepad resting on his knees. "We're very cost-...
7
votes
2answers
1k views

An Accountant Seeks the Help of a Mathematician

The accountant complaints to the mathematician: “I lent money to five other faculty members and still haven’t been paid back. You are one of them; the other four owe me 12 dollars altogether, but ...
15
votes
3answers
2k views

Four buttons on a table

I was asked lately (in an interview) to solve this puzzle, which is similar to the 4 cups on table puzzle. In a certain room there is a rotating round table, with 4 symmetrically located ...
0
votes
0answers
57 views

Electric switch [duplicate]

There are 3 switches in a room and a bulb in another room far away. One of the switches turns the bulb on. How can you find the switch which turns the bulb on by going to the room only once?
7
votes
1answer
518 views

Who attempted to betray the Boston King?

The Castle of Weshire recently declared war on the Castle of Boston. The two armies soon met, the Boston King and Weshire King giving out orders from behind their lines of soldiers, surround by their ...
-1
votes
0answers
73 views

Can all sudoku puzzles be solved “logically”? (I define what this means) [duplicate]

The top answer in the question below stated that it depends on how you define "logically": Are there published Sudoku puzzles that require guessing? It seems to me that what people refer to as "...
1
vote
2answers
5k views

Missing is what in picture

Source: http://gpuzzles.com/mind-teasers/pattern-series-picture-puzzle/?source=stack What is missing in the picture?
4
votes
2answers
210 views

What's the problem with the prisoner to be hanged logic puzzle

A criminal is imprisoned on Monday, and told "you will have been hanged by the weekend, but you won't know which day we'll hang you." If it gets to Thursday midnight and he's not been hanged yet, he ...
2
votes
1answer
830 views

Possible answer to the Heaven Hell Door riddle

There is a fairly common riddle You're standing between the door to heaven and the door to hell. A guard stands by each door. One guard always tells the truth, and the other always lies. You don't ...
3
votes
3answers
368 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, ...
8
votes
2answers
298 views

Poisoned Glasses on a Platter

Three identical, mute triplets, $F$, $S$, and $T$, each of whom is a perfect logician, have been kidnapped. Their captor begins by instructing them that in a room that they will shortly enter, are six ...
-3
votes
3answers
235 views

Only one option is correct [closed]

$a \in \mathbb{C}$ Which is the correct option: 1) $a = 1$ 2) $a = 42$ 3) $a = i =\sqrt{-1}$ 4) $0^a \in \mathbb{C}$ 5) $a^3 = 1$ Hint 1: Hint 2:
2
votes
1answer
130 views

Binary Bob's Programming Language Puzzle

Binary Bob Needs Your Assistance Bob's Dilemma Binary Bob is considering going back to school to learn computer programming, however, Bob has been given some jumbled course information. Bob needs ...
65
votes
26answers
14k views

You have one question to tell whether the number I'm thinking of is 1, 2, or 3

This is an interesting puzzle which was passed to me by a friend some time ago. I do know the answer, but will refrain from self-answering on this to see where it goes. I'm thinking of a number: 1, 2,...
3
votes
1answer
159 views

$n$ buttons on a table

A generalization of Four buttons on a table: In a certain room there is a rotating round table, with 4 symmetrically located indistinguishable buttons. Each button can be either ”on” or ”off”, ...
3
votes
3answers
326 views

Word Cipher with seemingly random numbers

I came across this interesting puzzle and have failed to crack it for more than three days. Can you solve it? m.imdb.com/title/tt2039338/ L=9, 20, [2x5], 6, 17, 13 W=38 The only tips I ...
2
votes
1answer
131 views

Tokyo Metro puzzle special #2: The tour of the Metro

This is a simpler puzzle: How many stations do you have to pass by to pass by every station of the Metro? map Please either 1) explain your solution or 2) make an image of the route. Once consensus ...
2
votes
1answer
184 views

Pattern recognition puzzle, …$5$ , M , $6,5040,$ … ; then M=?

The following pattern puzzle problem was given to me by one of my friend: $$\color{red}{5}$$ $$\color{blue}{24 \quad \quad \quad \text{M}}$$ $$\color{red}{4 \quad \quad \quad \quad \quad 6}$$ $...
0
votes
2answers
153 views

Pattern recognition problem: if $2 \star 8 \star 8 = 161642\dots$ then M=?

The following sequence was given to me by one of my friend: $$\color{red}{2 \star 8 \star 8 = 161642}$$ $$\color{blue}{4 \star 9 \star 7 = 362843}$$ $$\color{red}{7 \star 5 \star 9 = 356344}$$ ...
2
votes
2answers
121 views

Tokyo Metro puzzle special: Oops, the lines are coming down

Here is my first Special Edition puzzle, and it is a little harder. The map is also available as a PDF. So you, being a Tokyo straphanger, was in between Hikawadai (Y05 F05) and Kotake-mukaihara (...
8
votes
3answers
1k views

A first choice die

You and your friend have met to play a game of dice. This is a very simple game where both players roll a die at the same time, and the player with the lower score pays a coin to the other player. In ...
4
votes
1answer
128 views

Minesweeper challenge #5

Coming back to another Minesweeper challenge... I've run into another "unsolvable corner" (corner of a puzzle where there isn't enough information to be 100% certain that any particular square that ...
-5
votes
0answers
157 views

Numerical sequence help

I need help to solve this problem — I need to find the numbers that complete this sequence: 11, 89, 17, ?, 47, 62, ?, 10, 0 I have tried to solve it in many different ways but nothing came ...
2
votes
2answers
230 views

Unlock an answering machine using minimum number of digits

You know of answering machines with a remote inquiry facility, where you can call the answering machine and enter a four digit passcode into your telephone keypad, so you can listen to your messages ...
14
votes
3answers
699 views

Treasure Hunt Riddle

John and Peter participate in a treasure hunting competition. The organizer places a gold medal in one of the lockers. The locker rack contains 49 lockers, each of which has a name indicating its row ...
7
votes
3answers
438 views

Guess simultaneously, color of your hat, no passing allowed

1000 logicians standing in a circle are blindfolded and a hat of either black or white color is placed on each person's head. The blindfolds are then removed and each person can now see everybody's ...
8
votes
2answers
368 views

Houses and Telephone #s

There are 16 houses consecutively numbered 1-16. All houses have 7-digit telephone numbers, numbered consecutively, in the same order. For example, if house #3's phone number is 1111111, house #4 will ...
4
votes
1answer
194 views

systematic number removal [duplicate]

The whole, natural numbers 1 through 50 are written on a board. The following operation is performed 49 times: select any two of the numbers on the board and write the absolute value of their ...
4
votes
1answer
381 views

Analyzing Single-Elimination Tournaments

I know there are many questions/answers about single elimination tournaments out there, but I wanted to approach this question in a more holistic way. For a single-elimination tournament with N ...
7
votes
2answers
242 views

Integers in Cells puzzle (sudoko-like)

All the whole numbers 1−9 are placed in the 9 triangular cells. A negative sign is placed in front of some numbers. The letters A−F are products of 3 or 5 of the numbers. Find all possible ...
24
votes
5answers
4k views

The No-Straight Maze

Consider the following maze. You can walk on the black lines, and your aim is to go from the green at the maze's bottom to the red on the left side. However, each time you reach an intersection of ...
9
votes
2answers
6k views

Crack the 5 digits code

I created this "crack the code" puzzle. I hope the members here like it.
34
votes
16answers
5k views

XKCD inspired logic puzzle

I came up with a logic puzzle inspired by this xkcd comic. I don't yet have an answer, and I am wondering if anyone can come up with one. You are in a room with three doors. Two of the doors lead ...
4
votes
4answers
2k views

Generate the number for Sunday by finding the pattern

I found this puzzle on another site so I put it here to share with you. I will give link for the pattern logic of given puzzle. Answer: Click here
13
votes
2answers
6k views

The Harry Potter Potions Riddle

A simple riddle from the first Harry Potter book. You are in a room with seven potions. There is a doorway ahead and a doorway behind, both engulfed in flames. Which potion will allow you to move ...
6
votes
2answers
319 views

Find the Rogue with AOE

You are playing World of Warcraft which is well known an old MMORPG game. You are in arena where you play against another player. You are a mage and the opponent is a rogue which can hide while moving ...
9
votes
2answers
305 views

A weird number system (I made it myself)

So, I'm an eccentric mathematician. You can see this with my number system. I'm pulling a sneaky on you, and you'll have to tell me what everything means. I'm not telling you a thing: figure it for ...
0
votes
2answers
315 views

Numerical sequence

I need help in solving this sequence: ?, 36, 36, 18, 16, 14, ? I've tried to notice a pattern and saw that 7*2=14 8*2=16, 9×2=18 18×2=36 but after 9x2 the sequence doesn't make sense. I've also ...
7
votes
2answers
872 views

Hat puzzle - 7 prisoners

There are 7 prisoners buried up to their necks in sand. 6 are on one side of a wall, all facing the wall. They are lined up such that the furthest from the wall can see the 5 prisoners closest to the ...