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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-5
votes
1answer
183 views

Humphrey meets Laureen in town

Laureen is talking with Humphrey: "if the weather is good on Sunday I will go to the horse races. I will also bring my friend Sam with me, if he feels ok". on Sunday afternoon Humphrey meets Laureen ...
53
votes
4answers
5k views

Is this chromatic puzzle always solvable?

I've created a new puzzle from an Alexey Nigin's idea. It consists of a 8x8 board where each square is randomly assigned one of three colors. A movement is defined by picking any two orthogonal ...
-1
votes
2answers
310 views

Nothing is impossible

Here's a little logic-puzzle that I've been thinking about for years and I wanted to hear you oppinion: If nothing was impossible, wouldn't it be impossible to find something that is impossible?
0
votes
0answers
114 views

About the 100 blue eyes problem [duplicate]

I thought I understood your answer and liked it, but just read a different explanation at http://thesilentknight.info/2016/flawed-logic-blue-spot-problem/ that suggests that the 100 people would all ...
17
votes
5answers
4k views

Statements that the deities True and False cannot say

You over exert yourself working on logic puzzles and die of exhaustion. You are awoken by the omniscient deities True and False. True only speaks true statements and False only speaks false statements....
5
votes
3answers
2k views

Puzzle of Alphabet addition

This is an alphametic - Each of the alphabets in the below represents a unique digit in base 10 such that the following representation holds true. ...
-3
votes
2answers
254 views

Amazing sudoku who can find hot numbers

Sudoku X Place the numbers 1-6 once in every row, column, diagonal, and 3x2 block. The diagonals form an X and are highlighted. Puzzle Text of puzzle ----------------- | . . . | 5 . . | | . . . | ...
0
votes
1answer
490 views

The three girls [duplicate]

A man gets to know his neighbor, and he learns that she has 3 girls. Intrigued, he asks for their age. The lady, who doesn't want to give him this information straight away, has him to take a guess. ...
18
votes
8answers
3k views

What Imprisonment sentence will immortal citizen soldier Guilt receive?

On planet Immortal, everyone lives forever but essential resources (including food and supplies) on the planet are limited. Ultimatopian raiding swords are the most effective weapon available to loot ...
30
votes
5answers
4k views

Color elimination puzzle

You have a 5x5 board with on each cell a light that can be red, green or blue. Next to each row and each column there is a button that when pressed makes all red lights in that row/column green, all ...
20
votes
1answer
554 views

The Drouble with Doorples

You are the first officer aboard the Starship Enterpuzz, and moments after your captain departs for his week-long vacation, you discover that your ship is infested with tiny creatures called doorples. ...
2
votes
3answers
1k views

Puzzle to find one good person [duplicate]

There are 15 people who may lie or say the truth(bad people) and 16 people who will always say the truth(good) . Suppose A- bad person , B-good person and C-bad person, when asked about A, B will say ...
6
votes
2answers
348 views

Last in line at Diogenes's

Infinitely many (ℵo) philosophers came to Diogenes's Roadhouse for a night of unbridled belaboring. $ \require{begingroup} \begingroup \def \F {{ \sf\scriptsize F }} \def \...
8
votes
3answers
2k views

Infinite choice question

The assertions in the following infinite list are all the same, true or false.       $~\vdots$   T$~~$F $~~$ I have a black Model T.   T$~~$F $~~$ I have a black ...
1
vote
0answers
149 views

Can anyone solve this problem called the “Three Gods”? [duplicate]

Three gods True, False, and Random are called, in no particular order. True always speaks truly, False always speaks falsely, but whether Random speaks truly or falsely is a completely random matter. ...
14
votes
7answers
4k views

Find out the number using three clues

I was asked this question about finding a number and three clues were given which are as follows. If this number is multiple of 5, it would lie between 1 to 19. If this number is not multiple of 8, ...
6
votes
2answers
834 views

Pirate's Golden Throw

Five pirates are parting ways after finding a treasure of 100 pieces of gold. The pirates decide to split it based on a vote. Each pirate, from oldest to youngest, gets to propose a plan on how to ...
-2
votes
1answer
193 views

Age of the Daughters [duplicate]

Two Cambridge graduates, Peter and Paul, meet for the first time in 20 years. Peter asks, "How've you been?" Paul says, "Great! I'm married now and have three daughters." Peter asks, "How old are they?...
1
vote
2answers
2k views

Who is the killer? [duplicate]

Keeping it short and crisp. A man was murdered in his office. The suspects are Gerry, Joseph, Jason, Nick, James and Sophie. The numbers 6, 4, 9, 10, 11 are written on a calendar with ...
13
votes
7answers
2k views

Confused clock face puzzle

There is a clock face with the correct (target) numbers written in circles. But somebody confused the clock face and created a crazy clock with numbers written in ellipses. Your task is to repair ...
3
votes
2answers
190 views

Order the elements of this set using the clues provided

We must order the elements A, B, C, D, and E. We are told about the ordering A B C D E None of the elements are in their correct positions and none of the elements above correctly follow their ...
0
votes
4answers
1k views

Least number of Questions [duplicate]

If I write down a double digit number (10-99) and you have to guess the number by asking me the least number of questions regarding it, how will you do it? For example: You could start by asking is ...
6
votes
1answer
456 views

What changes can be made to make Matthew happy?

When Matthew eats at a buffet, he has one serving of each dish, but never goes back for seconds. When asked the name of his favorite animal, Matthew lists 26, each starting with a different letter. ...
5
votes
1answer
285 views

Extension of Four Is Cosmic

The fact that four is cosmic, at least in English, is quite well discussed. However, what if we instead took a number and then took the first letter of its word form that number and converted it to ...
8
votes
3answers
483 views

The Twins and the Number of Candies

Yveti and Xerni are twins. Their mischievous friend, Cubo, one day decides to give them a riddle. Cubo comes up to them and says, "I have two bags of candies in my bag. The first of you two to guess ...
7
votes
1answer
1k views

Help an athlete impress a math geek

Help Lucy impress Nick the math geek and find his apartment number! Lucy a track athlete, really likes Nick, a math geek. Nick is having a party at his apartment on Saturday and invites Lucy. Lucy ...
7
votes
2answers
736 views

What are the chances you lost a nickel?

Yesterday you had 50 coins totaling exactly one US dollar in value. Somehow you lost one of those fifty coins on the way to the vending machine. Assume the likelihood of losing each coin (regardless ...
2
votes
4answers
1k views

Time to speed up [closed]

Mr. X lives in A-City and wants to visit B-city. There are 1000 km between these 2 cities. So, Mr. X takes his car and drives to go to B-City. At halfway of his ride (500 km), he realises that his ...
7
votes
5answers
1k views

No ordinary magic square

Instead of placing every number from 1-9 in the square below such that each column, row and long diagonal has the same sum, do the opposite! Place 1-9 in the squares below in a manner such that none ...
5
votes
1answer
4k views

The Two Switches

11 prisoners arrive at a jail. But this jail is not an ordinary jail, it's a jail whose Warden despises ignorance and reveres wisdom. So much so, that the Warden is willing to free the group of ...
4
votes
1answer
299 views

The kids moved when we were gone! What is the likelihood that white is winning?

Two friends were playing a friendly game of chess. The both have young children who they recently taught the rules and they agreed both children could help if they wished. In the position below (...
4
votes
2answers
651 views

Switcheroo #2 - Monty Hall

Coming off of my last Switcheroo puzzle, here's another similar one in which you have to figure out the maximum number of options for the riddle. The Monty Hall problem goes as follows: you're on a ...
6
votes
2answers
664 views

Switcheroo - Which switch turns on the light bulb?

There is a famous puzzle, asked several times on this site, regarding a light bulb hidden in a room. There are three switches outside. You can flip them however you want, but you cannot continue ...
-1
votes
5answers
784 views

Correct way to add 22 to 4 to get 613867

Inspired by this, this, and this. I'm not great at math, I'll admit. However, I am quite sure that there is a way to add 22 to 4 to obtain the number 613867. Now, that's a pretty big number, so my ...
8
votes
7answers
878 views

Reverse puzzling - What is my brother solving?

This puzzle is inspired by the previous reverse puzzles My brother and I love puzzles. But I know he is solving some puzzles without me. So yesterday I sneaked into his bedroom to find out what he is ...
26
votes
4answers
1k views

Reverse Puzzling 4

[This continues prior Reverse Puzzling here, here and here] George rubbed his hands together with glee. "So this is Andrea's puzzle, is it?" "Yes," I answered. "It's the first of them, anyway." "...
45
votes
2answers
4k views

Reverse Puzzling

George is a great puzzler, so I was extremely surprised when he didn't immediately know the answer to a really famous puzzle. It's a puzzle that you probably did years ago, and have heard so often ...
0
votes
1answer
153 views

Not as tedious as it looks [duplicate]

Given the sequences: 1000, 11, 6, 3, 5, 4 1 000 000, 7, 5, 4 993, 25, 10, 3, 5, 4 1513, 32, 9, 4 What are the next hundred numbers in the sequence starting at 0? What are the first 6 terms ...
7
votes
2answers
340 views

Where the water is hotter

There are two perfectly identical boilers containing the same amount of water, switched on and working in identical environments. Both are setup so that the heating starts when the temperature of ...
12
votes
8answers
2k views

The Dot-town suicide

Each resident of Dot-town carries a red or blue dot on his (or her) forehead, but if he ever figures out what color it is he kills himself. Each day the residents gather; one day a stranger comes and ...
0
votes
2answers
458 views

Vacuum Salesman [duplicate]

A vacuum salesman rings on the door of a woman, trying to sell her a vacuum. The woman declines the continous offers and gets annoyed by the persistent salesman. She eventually offers to buy a vacuum ...
2
votes
8answers
577 views

5 logicians with 1 or 2 hats (Part II) [8,9,10]

This is the corrected version of this question. There are 5 logicians seated around a table. They are blindfolded and hats are placed on their heads. After removing the blindfolds, they are told a ...
2
votes
4answers
233 views

Create a special Playing Schedule - Logical/Mathematical Solution

Last Week in Training (I'm a Cycleball player) a logial problem/puzzle tricked us. And I'm wondering if there exists a logical solution for the next time. Cycleball is played in pairs (2 Players vs. ...
7
votes
3answers
666 views

Correct way to add 3 to sum(1/k!) to get 8

The recent spat of 22+4 puzzles took me back to 1974, when my high school math teacher (and cross-country coach), Dr James Quinlan, asked us to solve $$3+\sum_{k=0}^\infty \dfrac{1}{k!} = 8$$.
1
vote
7answers
886 views

Correct way to add 22 to 4 to get 70

Based on the other "Correct way to add 22 to 4" puzzles. Tell me the correct way to add 22 to 4 to get 70 As in the other puzzles, all numbers are in Base 10.
-2
votes
1answer
303 views

Mathematical Puzzle

1 * 1 = 1 2 * 13 = 2 3 * 3 = 3 44 * 8 = 4 73 * 5 = 0 90 * 60 = 0 Q1) What is the smallest set of numbers under this operation that can equal 5? 6? Q2) What is 8 * 9? Hint:
-2
votes
2answers
374 views

Correct way to add 22 to 4 to get 26

Inspired by five other puzzles, how could it be possible that in base $\pi$ adding 22 to 4 gives 26? What is the correct way to do it? Unlike all of the other puzzles, consider these numbers in base $...
3
votes
2answers
487 views

Correct way to add 22 to 4 to get 9999

Inspired by four other puzzles, how could it be possible that adding 22 to 4 gives 9999? What is the correct way to do it? As with all of the other puzzles, consider these numbers in base 10.
5
votes
1answer
419 views

The truth and lie mess

There are two persons with special traits such that : One speaks only lies and no truth on Monday, Tuesday and Wednesday and all truth rest of the week. The other speaks only lies and no truth on ...
4
votes
1answer
344 views

Correct way to add 22 to 4 to get two different results

Inspired by these series of puzzles, tell me a correct way by which adding 22 to 4 will give either 495 or 505. As in the other puzzles, these numbers are all expressed in base 10.

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33 34
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36 37
46