# 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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490 views

### Plants vs Zombies!

Several plants and zombies (no more than 20 creatures in total) came to the party “Plants VS Zombies”, and it turned out that all the creatures are of different heights. When a plant speaks to a lower ...
3k views

### How many smurfs are there?

Papa Smurf gathered some berries from the forest to the village and smurfs ate all those berries: The smurf who ate the most actually ate one-fourth of the berries eaten by the rest of the smurfs. ...
1k views

### A new puzzle - Sudoku X V

If someone is able to find the solution... I found 2,3,8 on line 5, column 3-4-5, but after that I am blocked, it looks too difficult for me.
900 views

### Calculation Sudoku

Here is a new quiz from my daily quiz calendar. I'm trying to find a way to solve it. The numbers 1-6 should be filled in. And like a sudoku, each row and each column should contain each number ...
162 views

### 9 people sitting at a round table

I am unable to figure out how to solve this question @Joffan has given an answer but he hasn't mentioned much regarding his approach. I requested him but he still didn't give a clear answer. This is ...
531 views

Rules of Slitherlink: Connect adjacent dots with vertical or horizontal lines to make a single loop. The numbers indicate how many lines surround it, while empty cells may be surrounded by any number ...
126 views

### Skyscrapers 7x7 How to get next Skyscraper on field

I have the following Skyscrapers puzzle: C3 C1 C2 C3 C4 C4 C2 C2 V3 C5 C4 V1 C1 C3 C4 C2 V5 C3 C3 V7 C3 C3 V4 V2 C2 C1 V2 C2 C1 C3 C4 C2 C2 C2 C2 C -> Clues how many ...
627 views

### I'm Bad at Naming Things, so Just Try to Solve this Patterned Masyu Puzzle!

The original Masyu rules apply. 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 ...
740 views

### Beating at Eating, a logic-grid puzzle for literal logicians

Name Surname Dessert 1 Agatha Greed cream puffs 2 Bugsy Forager trifle 3 Delilah Eatalot cheesecake 4 Chuck Hunk ice cream Four friends held a competition to see who could eat the greatest amount ...
664 views

### Distance Puzzle

The rules are: 1. Draw two circles (O) in the empty cells in every row and column. 2. The numbers in the black cells indicate the space between the 2 circles in the black cells' row or column, in ...
390 views

### A constrained, but concerning, celestial confrontation

An entry in Fortnightly Topic Challenge #52: Polyominoes. This puzzle is a hybrid between Pentominous and Star Battle. Your job is to divide the grid below into pentominoes according to the rules of ...
113 views

### Next Move on this Sudoku Classic

What would be the next move? Link to this sudoku
126 views

### Five possible liars - any way to solve with a grid-based method?

The situation is as follows: At a semiconductor laboratory in Hsinchu a security guard caught five technicians accessing a high level security area reserved for the most trusted scientists working in ...
983 views

### 2 fake coins from a pile of 30 coins

You need to find two fake coins from a pile of 30 coins. You know that a fake coin has a different weight to a real coin, but you don't know whether it is lighter or heavier. You also know that all ...
18k views

### Puzzle: Who hacked the computer?

I was working my way through some Knight and Knave Puzzles in Discrete Maths by Rosen, when I came across the following question: Four friends have been identified as suspects for an unauthorized ...
18k 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,...
8k views

### The coolest checkerboard magic trick

In the small town of Terni (Italy), there's a couple of young friends named Marco and Leonardo, who like to perform magic tricks to a restricted audience of common friends and relatives. They like to ...
424 views

### Baggage Mishap Logic Grid

This is a puzzle from Braingle: Savannah got distracted when her shuttle arrived at Earth Central Airport. Now she's at Lost & Found with four other travelers all waiting to retrieve one lost ...
190 views

### 3 weird images from a friend

I got sent this from a year ago, and I am still thinking what was the secret number that they hid a secret from, so here are the pictures. The first one was a car, and a random equation. The next one ...
287 views

### How old is Brenda?

Five friends (Adele, Brenda, Carol, Dana and Emily) were born peculiarly in consecutive years. It is known from their diaries that: Carol was born 2 years before Dana and is not the oldest of them all....
792 views

### Why is the next Sudoku step a 6?

I used a step-by-step Sudoku solver for a puzzle in which I was stuck. However I don't understand how the next number (6) was found. Sudoku puzzle where I was stuck: Sudoku puzzle solved by one step ...
91 views

### 4-DominoBrane #002 “81”

Here is another domino puzzle. This is considerably easier than puzzle set earlier this week, and definitely doesn’t need bifurcation. This uses 4-Dominoes (all the normal dominoes, minus any with a 5 ...
122 views

### 4-DominoBrane Exclusive

Here is a smaller puzzle from the set of domino puzzles, I call DominoBrane. This uses 4-Dominoes (all the normal dominoes, minus any with a 5 or a 6). Each domino ...
295 views

### Tapa on a Penrose Tiling

An entry in Fortnightly Topic Challenge #51: Non-rectangular grids. This is a standard Tapa puzzle, on a non-standard Tapa grid...the "grid" is a Penrose tiling! Since the grid is not ...
235 views

### Slitherlink: The Couple of Question Marks

This is my first slitherlink puzzle. I made it myself. Feedback is appreciated! (I hope this one has a unique solution, unlike my other past puzzles, wink). Rules of Slitherlink (taken from Nikoli): ...
317 views

### Haisu: Schezo's Birthday

Rules of Haisu: Draw a path from S to G passing through all white cells exactly once by connecting the centres of adjacent cells. When the path passes over a number N, it is on its N-th entry to the ...
265 views

### Arrange candies without repeating pattern

The following puzzle had been posted before but I couldn't understand the only answer that was given there, which was by @neodne . So, I created this post asking someone to explain neodne's answer to ...
620 views

### One truthteller, one liar, and two randoms - least questions to identify?

I have landed on a new planet and there are 4 people there. One of them is a truth teller and they always speak the truth. The other is a liar and they always lie. The other 2 are random and they ...
161 views

### Swapping eggs puzzle

You can try this with pencil and paper, or make it a physical puzzle you can try out with your kids if you have one of those large 3x6 egg cartons laying around. Imagine you have 3 rows of 6 spots. ...
298 views

### The Nurikabe of Peace

Today is the 75th anniversary of Sir Winston Churchill's speech "The Sinews of Peace" which introduced to the world the phrase "The Iron Curtain". This puzzle is inspired by that ...
485 views

### Grid of numbers and dashes, X-Akseli and Y-Ehe?

I have been given this puzzle by my friend (who is a qualified military cryptographer). I am completely stuck as for what to do. They gave me this hint: "Don't take it so literal, think in all ...
431 views

### Escape from Sudoku!

An entry in Fortnightly Topic Challenge #50: Escape Rooms I hesitated to enter this in the Escape Room FTC, but I definitely was inspired by the challenge to create this puzzle, and it is, in some ...
222 views

### Double sudoku - two-digit numbers, the 1s and 10s places both form Sudokus [closed]

Using distinct 2-digit numbers from 11-99 that have no zeros, fill in the grid so that the tens digits form a Sudoku and the units digits form a (different) Sudoku. There might be a mathematical way ...
773 views

### Sorting 6 boxes by selecting 3 boxes each time

There are 6 boxes, each containing a distinct number. You can select 3 boxes and the Oracle will tell you which box has the smallest number and which has the largest number of the three selected boxes....
200 views

### Another (simple) self-referential aptitude test

Nine months ago I started my journey on Puzzling in a rough way with this question. I honesty hope this time I won't generate so extended discussion...! I love self-referential questions, puzzles or ...
559 views

### Shingoki: An Exploration of Unicode

An entry in Fortnightly Topic Challenge #42: Wordless Connecting Walls-- wait, what? This is a Shingoki puzzle. The rules (paraphrased from puzzle-shingoki.com) are as follows: The aim is to form a ...
4k views

### How to get 32 by using +1 , +1 , ×3 , ×3 , ÷2 , ÷2, ^2, ^2?

How to get 32 by using +1,+1,×3,×3,÷2,÷2,^2,^2? (The last two operators are 'squaring'.)
156 views

### I need some help with this 15x15 nonogram

I have been working on this nonogram for some time and can't seen to figure out what to do next... This is the link: https://nonograms-katana.com/play/#game
13k views

### 1 Fake Coin among N Amount of coins

You are given $N$ coins which consists of only $1$ fake coin. You also have a sensitive old-fashioned Pan Balance Scale. You are asked to find the fake coin in totally 5 times weighing on the Pan ...
233 views

### How to get the least possible sum in a closed loop set of squares?

The puzzle is as follows: The figure from below represents a set of 12 squares joined forming a closed loop. By using only the numbers from 1 to 12 fill in the blanks. The condition is that, without ...
224 views

### Nurikabe: The Terrible Tower of Threes!

This puzzle is a quick and fun little Nurikabe that is very tall, because I am not. It's not particularly tough, but if you need a nice relaxing grid-deduction puzzle to calm your brain today, this ...
394 views

### Trivia… sudoku

An entry in Fortnightly Topic Challenge #49: Pub Quiz Camouflage Please do not search the answers online (hence the no-computers tag), otherwise it would be too simple to solve this puzzle. I tried ...
114 views

### How to find the least number of extractions to make the word QATAR?

The riddle is as follows: A local library has lended its catalog card cabinet so it can be used in a raffle. The raffle prize is a luxurious travel to the Middle East for vacations to an employee ...
497 views

### Matches to move in order to get right roman numeral over fifty

The riddle is as follows: The figure from below represents a set of roman numerals wrote in such a way that the sum is not correct. The numbers are arranged as: 50+12=51 How many matches minimum ...
502 views

### 3 travelers and 9 diamonds

There are three travelers. They are inside a cave. Deep down in this cave, there are three doors, each door containing at least one diamond, and there are a total of 9 diamonds. Each traveler picks a ...
113 views

### How many have to enter the building so their birthday matches?

The riddle is as follows: Looking at his watch a doorman from an hotel in New York notices that 280 people are inside. Suddenly he begins to ponder the following. How many people should have to come ...
142 views

### Seven letters riddle

Hoping it is a never-seen riddle, here is the problem. We have seven letters A,B,C,D,E,F,G. Each letter is associated with a unique number between 1 and 10. We know the following: D is 3 units ...
430 views

### We have captured 5 spies. Their names are A, B, C, D, and E

This is a variant of the puzzle here. We have captured 5 spies belonging to a secret organization. Their identities are unknown; we only know them by their codenames A, B, C, D, and E. After thorough ...