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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).

-3
votes
0answers
59 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 ...
6
votes
4answers
218 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
341 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 ...
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
168 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 ...
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 ...
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?
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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 "...
11
votes
3answers
619 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-...
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, ...
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 ...
-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:
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
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”, ...
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
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: $$\color{red}{2 \star 8 \star 8 = 161642}$$ $$\color{blue}{4 \star 9 \star 7 = 362843}$$ $$\color{red}{7 \star 5 \star 9 = 356344}$$ ...
7
votes
1answer
519 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 ...
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: $$\color{red}{5}$$ $$\color{blue}{24 \quad \quad \quad \text{M}}$$ $$\color{red}{4 \quad \quad \quad \quad \quad 6}$$ $...
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 (...
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
158 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 ...
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 ...
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 ...
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 ...
0
votes
1answer
137 views

How many trees and birds are there? [closed]

There are 'X' number of Trees and 'Y' number Birds. If 1 bird sits on each tree then 1 BIRD will be left. If 2 birds sits on each tree then 1 TREE will be left. What is number of trees(X) and ...
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 ...
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 ...
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 ...
5
votes
1answer
242 views

Stuck in 6x6 skyscraper puzzle

I don't know how to continue, can anyone tell me which next number am I able to add? Here is the puzzle (there are clues at edges), and below are possibilities. Feel free to tell me if I made mistake, ...
4
votes
4answers
246 views

Weighing Counterfeit coins

There are $n=4$ coins and we know exactly $2$ of them are counterfeit. In $2$ weighings, how can we find which of the four coins are the counterfeit ones? Assumptions: the counterfeit coins look ...
11
votes
3answers
3k views

Where did they find Gold?

A lesson in US Colonial history. ( A stretched version) After the thirteen colonies declared independence they needed resources badly. So the enterprising brave pioneers of those times set out to ...
0
votes
1answer
177 views

Who's the killer? [closed]

When the elevator man saw Mr. Kelley, Mr. Kelley was bleeding slightly, but he did not seem too badly hurt. Mr. Kelley had destroyed Mr. Jones’ business by stealing all of his customers. The ...
2
votes
1answer
173 views

People having different ages residing on different floors of a building

Here is the riddle: Eight people, 'A', 'B', 'C', 'D', 'E', 'F', 'G', and 'H' live in an eight–story building. The lowest floor is numbered '1' and the topmost floor is numbered '8'. The ...
0
votes
2answers
179 views

Boxes stacked one above the other

Eight boxes, A, B, C, D, E, F, G, and H are kept one above another not necessarily in the order above. Three boxes are between H and G and neither of them is at the top or bottom position. ...
5
votes
3answers
220 views

Four squares into many squares

You are given four unit squares and your task is to form as many rectangles as possible out of it starting from 1 square (by overlapping every squares into each other) to N, one by one (2,3,4...). So ...
5
votes
6answers
332 views

A Gambling Problem You Would Love To Have

Let's play a quick gambling game You are going to start by betting a penny, and then I roll a 10-sided die. It is labeled 0 through 9. Whatever you roll, that's what I multiply your bet by and give ...
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 ...
5
votes
1answer
108 views

To all you Game lovers

If BACKGAMMON is reverse of CONNECT4 And OTHELLO is BACKGAMMON and MONOPOLY together Then TRIVIAL PURSUIT is OTHELLO and what together? The "what" is of course a sit down game! ...
16
votes
0answers
455 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 ...
11
votes
2answers
275 views

Pucks in the arena

Two identical pucks of radius 10 cm are placed in a round arena of radius 1 m. They are positioned 50 cm away from the center of the arena on opposing sides. Assuming no energy losses during sliding ...
4
votes
2answers
261 views

A locked room puzzle

“They’re in the drawing room, Sir,” said the constable who was waiting outside the doors. The house — perhaps mansion was a better word — was a square, four storey building in two acres of grounds. ...
0
votes
2answers
158 views

Shopping Spree - Simple Logic Puzzle

The Hello World of Grid Based Logic Puzzles Shopping Spree Bill and Mary went shopping. They brought home a TV, and a new Tablet, one cost 100, the other 200. One transaction was paid in cash, the ...
1
vote
1answer
119 views

Can you help our Puzzle Heroe's with their amnesia?

DISASTER HAS STRUCK!!! Our Stack O' Puzzle Heroe's have amnesia! It happened last night, when each one of the puzzle heroes' arch-nemesis defeated them all by giving them all AMNESIA! They all lost ...
6
votes
3answers
973 views

Knights Problem

There are 2 white knights and 2 black knights positioned at a (3 X 3) chess board. Find the minimum number of moves required to ...
3
votes
6answers
334 views

Beginner Logic Puzzle - Web Site Log

I recently began creating my own logic puzzles. I thought I'd share some, from easy to hard here. Here is an easy one to get you warmed up! Puzzle Information A group of friends - John, Heather, and ...
6
votes
5answers
250 views

Book Lenders Puzzle (Answer with the least amount of steps in 5 days wins!)

You are a Book lender who strangely lends books of equal length and difficulty ever time. You have people who you lend your books to, but you want to find out who is the fastest reader of the group ...