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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).

4
votes
4answers
1k 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]{...
9
votes
5answers
1k 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 ...
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 ...
3
votes
5answers
299 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 ...
40
votes
11answers
7k 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
3answers
257 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.
2
votes
1answer
128 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 \...
-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
4answers
154 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 ...
-3
votes
0answers
178 views

IQ test question from Vietnam [duplicate]

If anyone know how to do it? Confuse from https://testiq.vn/iq-test.html
4
votes
2answers
267 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 ...
27
votes
12answers
2k views

Shapes and letters. What is the missing box?

Finally, someone has figured it out. Good job.
5
votes
3answers
255 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
176 views

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

The following pattern was given to me by one of my friend: $$\color{red}{224}$$ $$14 \quad \quad 8$$ $$4 \quad \quad \quad \quad \quad 3$$ $$8 \quad \quad \quad \quad \quad \quad \quad 4$$ $...
7
votes
3answers
375 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 ...
21
votes
8answers
1k 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 ...
-2
votes
0answers
409 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.
9
votes
2answers
293 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....
8
votes
2answers
244 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 ...
7
votes
4answers
296 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 ...
13
votes
1answer
404 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
305 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
183 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 ...
20
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?
11
votes
3answers
648 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
222 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
885 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 ...
5
votes
5answers
637 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
151 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
239 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
310 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
175 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”, ...
16
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
160 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
542 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
158 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
190 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
127 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
135 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 ...
14
votes
3answers
726 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
1answer
140 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
321 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
449 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
237 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
252 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
253 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 ...