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187
votes
7answers
19k views

My prefix is food, my suffix is rude

I thought of this riddle myself. Feedback is appreciated. My prefix is food. My suffix is rude. My infix comes in rounds. I keep you off the ground. What am I?
49
votes
4answers
8k views

Interview Question or Pathbreaking puzzle

I thought this changes the way series of numbers are looked at 1 1 1 2 1 1 2 1 1 Write down the next three lines
49
votes
9answers
71k views

Twelve balls and a scale

You are given twelve identical-looking balls and a two-sided scale. One of the balls is of a different weight, although you don't know whether it's lighter or heavier. How can you use just three ...
89
votes
15answers
881k views

Two doors with two guards - one lies, one tells the truth

You are a prisoner in a room with 2 doors and 2 guards. One of the doors will guide you to freedom and behind the other is a hangman --you don't know which is which. One of the guards always tells ...
30
votes
2answers
2k views

Introducing Gladys, an intrepid globetrotter

Gladys has always led an active life full of adventure. As a retiree, she has a lot of free time on her hands and loves to spend it on her two favourite pastimes – travelling and crossword ...
77
votes
1answer
6k views

Cryptic Clue Guide

This post is not a puzzle. There is nothing puzzly hidden inside it or the self-answer, posted at the same time. What exactly is a cryptic crossword clue, and how do I write one?
17
votes
2answers
7k views

A general solution to the decanting problem? (aka jug-pouring, water-pouring)

Take a look at these two questions: - A Set of Water Jug Challenges - Pouring problem Now I'm asking for a generalised solution to that problem. I define the problem as follows: You are required ...
62
votes
1answer
4k views

Word Riddle - you love me or you hate me

With two I’m affirmative With three I’m respectful With four I’m more respectful With all five I’m either loved or hated But when I’m loved, I kill; and when I’m hated, I may save lives.
163
votes
22answers
71k views

In the 100 blue eyes problem - why is the oracle necessary?

The riddle Randall Munroe (of xkcd fame) has, a bit hidden on his site, a logic puzzle: A group of people with assorted eye colors live on an island. They are all perfect logicians -- if a ...
30
votes
2answers
3k views

Determine the algorithm

So I was given this puzzle quite some time ago and just thought it would make a nice addition to this site: Your task is to determine the method how the result is determined from the given number. A ...
39
votes
5answers
5k views

Burning ropes as timers

You have 2 identical ropes which burn at a specific rate, and an unlimited supply of matches. When you light one end of a rope, the fire will take exactly 1 hour to travel to the other end of the rope....
40
votes
4answers
4k views

Which switch goes to which bulb?

You are in a room with three switches, labeled $A$, $B$, and $C$. Initially, each switch is in an off state. In an adjoining room, there are three incandescent light bulbs. Your task is to ...
20
votes
2answers
9k views

Coin weighing problem

You are given ten stacks of golden coins, each stack consisting of ten coins and a digital scale with arbitrary precision. You know that all stacks of coins are made from gold, weighing 10 grams per ...
25
votes
2answers
2k views

Where has the last dollar gone?

Lately I have found different versions of this puzzle, I was wondering if it has a name or belongs to a specific kind, so that I can understand it better. Here it is: Peter got \$10 from his father,...
45
votes
2answers
4k views

Four-words (----||||)

Four-words : My first is indivisible , but not really. My second is a cloak worn by men , but in ancient Rome. My third is a cruel wicked person , but not a human. My fourth is about 20 quires , but ...
7
votes
3answers
480 views

Tiling rectangles with F pentomino plus rectangles

Inspired by Polyomino Z pentomino and rectangle packing into rectangle Also in this series: Tiling rectangles with N pentomino plus rectangles Tiling rectangles with T pentomino plus rectangles ...
43
votes
6answers
28k views

Hats and Aliens

Here's a neat little puzzle taken from a Google interview question: 10 humans are abducted by aliens; each represents 10% of the entire human population. The aliens give each abductee either a ...
26
votes
7answers
11k views

The most words that can be made by successively adding one letter to the original word?

What is the largest number of words that can be made by just adding one letter to the original word, where each iteration is a meaningful word? E.g. ...
31
votes
5answers
16k views

Oh, it is greater than God!

What is greater than God, worse than evil, The poor have it, the rich require it, And if you eat it, you die? What is it?
14
votes
2answers
5k views

Riddle of the Unwanted Present

The one who made it didn't want it The one who bought it didn't need it The one who received it didn't wish for it The one who used it never saw it What was it?
75
votes
5answers
10k views

What characteristics of a ciphertext can be indicators of a particular cipher?

If I have a ciphertext, what information about the probable ciphers used can I infer from the ciphertext itself? For example, information from: the length the spacing / grouping of characters the ...
66
votes
26answers
14k 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,...
14
votes
5answers
5k views

N logicians wearing hats of N colors

N logicians are wearing hats which can be of N different colors (each hat has one color; there can be multiple hats with the same color). Each logician can see the colors of all hats except his own. ...
-6
votes
3answers
4k views

The Security to the Party [closed]

A party is being held at a local mansion. The host is very rich and his success is because of one thing ~ his famous recipe for Spaghetti! The only guests that may attend are people the host knows ...
23
votes
6answers
73k views

Make numbers 1 - 30 using the digits 2, 0, 1, 8

It's 2018 so let's repeat last year's challenge with new digits. This is similar to the "Four fours" puzzle, but using the digits 2, 0, 1 and 8. Rules: Use all four digits exactly once Allowed ...
18
votes
3answers
3k views

Knights and jokers

There are $N$ men. $K$ of them are knights, $M$ of them are jokers. $N$ is known, $K$ and $M$ are unknown. You know that: $K + M = N$, $K \gt M$, $M \ge 1$, $N$ is odd. Knights always tell ...
44
votes
3answers
11k views

I don't know the two numbers… but now I do

Two perfect logicians, Summer and Proctor, are told that integers $x$ and $y$ have been chosen such that $1 < x < y$ and $x+y < 100$. Summer is given the value $x+y$ and Proctor is given the ...
57
votes
10answers
42k views

A camel transporting bananas

A somewhat well-known puzzle is described as such: You have a pile of 3,000 bananas. You wish to transport them to a place 1,000 miles away on the back of a camel; however, the camel can only carry ...
27
votes
4answers
16k views

Learning to Solve a River Crossing Puzzle

I have seen many variations of the following puzzle: Once upon a time, a farmer went to the market and purchased a fox, a goose, and a bag of beans. On his way home, the farmer came to the bank of ...
30
votes
1answer
4k views

The hangman game backward

So, @JLee has posted a hangman game (Hangman- No misses left) on SE. I would like to create one too, but let's do it backward - guess what was the question, with only 1 letter missing: fill in an "a"...
25
votes
1answer
2k views

Four is Cosmic!

This is a little puzzle I heard a while back from one of my mathematically inclined friends- I get the sense that it's bounced around a little, so forgive me if you've heard it. There is a sort of ...
15
votes
4answers
31k views

Is it possible to use one sequence of moves to solve the Rubik's cube from any position?

Is there a sequence of moves that can be repeated over and over again which can solve any legal position the Rubik's Cube? If so what is it, and if there's more than one, what's the shortest? If not, ...
15
votes
5answers
2k views

Cards in the darkness

A man is sitting in a dark room. In front of him is a pile of 100 cards. He knows that there are 90 cards faced up and 10 cards faced down. Is it possible for the man to form two piles from these ...
10
votes
4answers
8k views

N balls and a scale

The question of twelve balls and a scale is probably the best-known example of the "find the ball of a different weight" problem. But does it generalize? Is there a general way to find a weighing ...
22
votes
4answers
3k views

The Monty Hall problem

I'm amazed that, although well known, this problem hasn't been posted yet. Monty Hall You are on a game show. The host of the show shows you three doors. He tells you that behind one of them, is a ...
19
votes
2answers
3k views

Alphabet splitting extraordinaire!

Here are three ways of splitting the letters of the English alphabet into two groups: 1) ABDOPQR; CEFGHIJKLMNSTUVWXYZ 2) BCDGJOPQRSU; AEFHIKLMNTVWXYZ 3) DFHIJLNOPRTUVXYZ; ABCEGKMQSW In each case, ...
5
votes
5answers
3k views

A Set of Water Jug Challenges

You've probably heard about challenges with water jugs, so why not try a few? Use 3- and 5- liter jugs to get 4 liters. Use 5- and 7- liter jugs to get 4 liters. This one's different. How many ...
22
votes
4answers
3k views

I am an expression of a deer mint - Clue One

You wake up one morning, and immediately look over at the letter on your bedside table. It reads: Dear [redacted]: You have been chosen to assemble the most powerful thing in the world - the [...
108
votes
6answers
23k views

100 Prisoners' Names in Boxes

Names in Boxes The names of 100 prisoners are placed in 100 wooden boxes, one name to a box, and the boxes are lined up on a table in a room. One by one, the prisoners are led into the room;...
40
votes
7answers
6k views

Guide to Codes and Ciphers

Note: This is a Guide not a Puzzle ciphers are quite common now on puzzling, and at first can seem quite confusing. But ciphers are bigger than this site, used worldwide by companies and secret ...
114
votes
9answers
18k views

Paying the Troll toll

You are on your way to visit your Grandma, who lives at the end of the valley. It's her birthday, and you want to give her the cakes you've made. Between your house and her house, you have to cross 7 ...
40
votes
5answers
23k views

A five card trick - How does it work?

At a party last night, my friends Alice and Bob did a magic trick. Any ideas how it worked? Alice shuffled a pack of cards, and asked me to take five. I looked at them. She put the rest of the pack ...
48
votes
11answers
251k views

6, the magic number

Here's a fun (albeit difficult) one: Make these equations true using arithmetic operations: ...
33
votes
3answers
5k views

Pirates and gold coins

A group of N pirates has come by a chest containing 200 gold coins. Their rules require that the coins be distributed by the following approach. The pirates are ranked from fiercest to meekest and ...
31
votes
4answers
18k views

Why is a single-corner twist not a valid position on a Rubik's cube?

For those of you familiar with the solution to the Rubik's cube, you will know that a single-corner twist is not a valid position. It can neither be attained by scrambling, nor can it be solved if it ...
5
votes
2answers
4k views

Techniques to Solve this Sudoku Puzzle

I have a sudoku puzzle seen below that I am trying to solve. I know I can punch this into some sudoku solver and get the answer but I am looking for techniques I can use to solve this. Any advice?
30
votes
7answers
5k views

Dinosaur egg drop

Archeologists discover two dinosaur eggs, and you are given the chance to test the durability of these eggs (bad move on their part). Suppose that these eggs will absorb a specific amount of force ...
19
votes
1answer
1k views

Community Metapuzzle - The Broken Time Machine

(This is the community metapuzzle, discussed in this meta thread. It requires answers from nine other puzzles linked below.) You find a mysterious device sitting on the ground. It's labelled in a ...
24
votes
5answers
1k views

Polyomino T hexomino and rectangle packing into rectangle

Let's pack some (one or more) T hexominoes together with some (one or more) small $a\times b$ rectangles into some bigger $m\times n$ rectangle without holes and overlapping pieces. For example, I ...
24
votes
4answers
719 views

Recycling old answers

Each of the puzzles below gives a two-word answer. Solve the puzzles and arrange the resulting 16 words into four groups of four, each with a common theme. The resulting group names form a clue for ...

15 30 50 per page