# 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).

2,601 questions
Filter by
Sorted by
Tagged with
0answers
62 views

### Connect the Balls [duplicate]

Draw only 4 lines join all the 9 balls. Hint- Bonus Question- Question Source
2answers
271 views

### Why are 2s not possible in these Sudoku cells?

I recently was playing Sudoku on my iPad. As I was stuck on the puzzle I clicked on "Tip" to receive a hint on how I can solve this Sudoku (I am still learning the game) - so please don't ...
0answers
82 views

### How do I solve a 1 to 9 puzzle? [closed]

This is a 1 to 9 puzzle, where the digits 1-9, each once, must be used to fill the boxes. Each row, column, and diagonal must add up to the number shown. What technique can be used to solve this kind ...
2answers
2k views

### Making a 9 digit number divisible by 11

Alice and Bob play the following game, taking turns. Alice starts and writes a non-zero single digit number at the blackboard. At every turn, each player adds a single digit at the right of the ...
1answer
400 views

### Knight or Knave

On the island of knights and knaves (where knights always tell the truth and knaves lie), you meet two islanders named Penny and Quinru. Penny: Both Quinru and I are knaves! Who is a knight and who ...
18answers
23k views

### Are there eighteen or twenty bars in my castle?

Two friends, Mark and Rose, are very famous logicians; they are so clever that they can deduce any logic connection possible in a matter of minutes even from the most vague situation. Unfortunately, ...
2answers
2k views

### Are there any sudoku puzzles combined with magic squares? [duplicate]

As everyone knows, in Sudoku the sum of each row and column is 45. So all Sudoku solutions are some kind of magic square. My question is: Has anyone seen a Sudoku puzzle combined with the magic square ...
1answer
836 views

### What is the fewest number of clues on a rotationally symmetrical sudoku grid with a unique solution?

It is known that the minimum number of clues a sudoku must have to have a unique solution is 17. But on every website I've seen for them, I haven't found any that are rotationally symmetrical. I once ...
13answers
21k views

### Protagoras's Paradox. An Unsolved Court Case

Many years ago, a Law teacher came across a student who was willing to learn but was unable to pay the fees.The student struck a deal saying, "I will pay your fee the day I win my first case in the ...
2answers
6k views

### Find the direction of the disc

You have a disc. One half of the disc is painted white and the other half is black. The disc rotates in either a clockwise direction or an anti-clockwise direction. There are two sensors which are ...
0answers
174 views

### Her granddaughter is the only daughter of my brother

Pointing to a woman, Abhijit said, "Her granddaughter is the only daughter of my brother." How is the woman related to Abhijit? Sister Grandmother Mother-in-law Mother Source of the ...
0answers
217 views

### Chess A Knight's Journey

You'll need to know about: A game that has existed for over 1500 years A game that doesn't exist ♞ → I → II → III → ... Answer = Xxxxxxxxx
2answers
321 views

### The Hallway and Tele Doors ~ Prolong the Inevitable

Sequel to: The Hallway and Tele Doors Note: You need not have to read the above to understand this puzzle, however this puzzle does spoil the above one. The tele door system: Each pair of doors, ...
1answer
583 views

### Flying pigs arrive

You’ve built pens for flying pigs. Being, well, flying pigs, they pick their own accommodation in full accordance to their preferences. Can you figure out what creature joined them? Pigs only occupy ...
1answer
2k views

### A Sudoku with only four given digits and some more rules

This is one of the hardest Sudokus (and one of the best Sudokus) I have ever seen, with only 4 given digits. There are some more rules too: First, normal Sudoku rules apply here. Both the diagonals ...
2answers
167 views

### Next step/strategies for an Area 51 (Slitherlink variant) puzzle

I've been doing quite a few Slitherlinks recently (and puzzles containing Slitherlink elements, such as Area 51). I'm familiar with all the patterns described in the Wiki article but I feel like there'...
1answer
81 views

### Finding a lock combination [closed]

Here is a puzzle that I recently encountered: You have a four digit lock with the following clues. When you enter 1378, one digit is correct and well-placed. When you enter 2834, nothing is correct. ...
2answers
922 views

### 13-by-13 SIKAKU puzzle

A SIKAKU puzzle consists of a square or rectangular grid in which some of the cells contain a one or two digit number. To complete the puzzle, a Solver must divide the puzzle into a number of ...
1answer
523 views

### Slitherknot (Double Slitherlink)

This is a variation on the classic Slitherlink Puzzle. However, instead of creating one loop, you must create 2 separate loops. The two loops can not share any edges, however they can cross or meet on ...
1answer
373 views

### Minimum amount of clues for a 16x16 sudoku

I know that 17 is the minimum for a standard 9x9 (3x3 squares), but what about a 16x16 (4x4 squares) sudoku?
1answer
1k views

### Beans under the chessboard

Under every grid cell of a chessboard, I put either one bean or nothing. Now if you choose a (grid) rectangular area on the chessboard, then I will tell you the parity of the number of beans under ...
1answer
93 views

### How is the boy related to the girl? [closed]

Pointing to a boy a girl said "He is the son of the daughter of the father of my only uncle. "How is the boy related to the girl?" A standard yet simple technique will be highly ...
4answers
2k views

### Who is the liar (Number of liars)?

There are 5 people. Each one can be lying or telling the truth, and they can't switch. Below, each person tells us how many liars exist in the group. There are at least 3 liars. There are at least 2 ...
5answers
2k views

### The 10 Logicians

There are two types of logicians: knights and knaves. Knights will always give a statement that is true whereas knaves will always give a statement that is false. After listening in on a conversation ...
2answers
426 views

### Blood relations in deducing family tree

Eight members of a family A,B,C,D,E,F,G and H are sitting around a circular table. Some of them are facing inside and some of them are facing outside. The couples are facing inside and singles are ...
2answers
213 views

### Four Mathematicians, Four Poker Hands and Four Clues

These four mathematician friends play poker every Saturday night. They always have a twist for the very last hand, just for fun. This Saturday the twist was “Factorial Clues”. The rule for the last ...
1answer
250 views

### 9x9 Sudoku Slitherlink Hybrid

I previously created a combined slitherlink and sukoku puzzle, but I was unsatisfied because the grid was smaller then a regular sudoku. So I made another, larger one. Below is a 9 by 9 grid. This is ...
1answer
200 views

### Gaps - Square Numbers

Rules of Gaps: Fill some cells with stars, so that each row and column contains exactly two stars. The stars cannot touch each other, not even diagonally. Numbers outside the grid indicate the number ...
1answer
92 views

1answer
958 views

### My grandfather's coins

When my grandfather died, he left his fine collection of coins, not more than 2500 of them, to his children, a different number to each of them, and in decreasing amounts according to their ages. To ...
1answer
435 views

### Windmill: A Masyu Puzzle

The standard Masyu rules apply.
0answers
53 views

### Mathematics based question [duplicate]

Vani meam has three Tatva books, one for chemistry, physics and biology. The chemistry book had 120 pages, the physics book has 10% more pages and the biology book has 10% fewer pages. In a class, she ...
1answer
68 views

### How to solve the attached sudoku?

Please explain the logic. I am not trying to solve it using trial and error or using any software. I am just looking for the next step. This sudoku is from apple 'Sudoku King' app.
0answers
50 views

### Grids with tiles of two colors and connectors

Make a square grid with an even side. Make a continuous trail which passes through all small squares; the trail ends where it started. Where there is an angle you can put a red or a blue tile. On ...
1answer
146 views

### How could I solve the attached Sudoku?

Please explain the logic. I am not trying to solve it using trial and error or using any software. I am just looking for the next step. This sudoku is from apple 'Sudoku King' app.
0answers
43 views

### Rickey Rat puzzle [duplicate]

A powerful sorcerer has hired Rickey Rat as an intern. The wizard gives Rick the task of carrying water from a well to the garden. The path from the well to the garden is up a staircase with 1000 ...
13answers
5k views

### Five hats and four logicians in a circle

I found this question in a book. The solution is correct (and complicated). No tricks involved. Four men were seated around a table. They were blindfolded and a colored hat was placed on each of ...
1answer
254 views

### Trapped in an escape room with 2 liars

You are in a room, with 6 people. 2 of them are liars. The room has a code pad. The people say: People What they say Keith The first and last digit are the same number and are not used anywhere else ...
3answers
2k views

### What is the age of the old man?

In autumn of the year 2003 an old man was asked about his age. He answered: "I was born on a Sunday morning in summer and I celebrated my seventh birthday on a Sunday morning too!" How old ...