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13
votes
1answer
2k views

How to solve this 7x8 grid with partially and completely filled squares?

I've tried looking at the paper from different angles, and nothing is jumping out at me. I'm not sure what to try next. Thanks!
15
votes
1answer
1k views

Touching matchsticks with compass and straightedge

The question Touching Matchsticks asked for the smallest matchstick graph where every node is connected to four distinct edges. The Harborth Graph is the smallest such, with 104 edges connecting 52 ...
21
votes
1answer
2k views

Riddle - He who holds the answer may enter

Here's a riddle I used in a game some time ago. Not the best riddle ever, but we had fun solving it. It was written on a translucent door, on the frame of which was written "He who holds the answer ...
25
votes
5answers
3k views

A mathematician's coffee alphametic

Alfréd Rényi, a Hungarian mathematician, said that a mathematician is a machine for turning coffee into theorems. It's believed that his mention was about his colleague, Paul Erdős, the celebrated ...
7
votes
5answers
3k views

3d x 1d = 2d x 2d

Find the largest integer that is a product of three-digit number and a one-digit number and also a product of two two-digit numbers. For example, 200 x 1 = 10 x 20. Of course, 200 is not the largest.
9
votes
1answer
1k views

Cryptic clue: Boil rocks in wood scrap (7)

I'm newbie to cryptic crosswords and I'm a bit lost as to how "abolish" is the answer to the clue "Boil rocks in wood scrap (7)."
4
votes
2answers
744 views

Puzzle pieces, each in contact with 5 others

You are asked to create puzzle pieces by joining together identical squares. This needs to be done such that the puzzle pieces can be arranged in a pattern with each piece being in contact with ...
12
votes
4answers
2k views

Four stones on a Go-board

On a standard $19\times19$ Go-board there are four stones: two white stones in the lower left and the upper right corner, and two black stones in the lower right and the upper left corner. Alice (...
7
votes
1answer
1k views

Probability of Seeing a Car in 10 Minutes & 30 Minutes [closed]

On a deserted road, the probability of observing a car during a thirty-minute period is 95%. What is the chance of observing a car in a ten-minute period? Hint: To clarify the question we are saying ...
10
votes
6answers
7k views

Aeroplane roundtrip in the wind

If an aeroplane makes a round trip and a wind is blowing, is the trip time shorter, longer or the same as without wind? Why? Round trip mean aeroplane go from point A to point B and then return to ...
13
votes
1answer
705 views

Three secret numbers (Variant 1 and Variant 2)

The statements of the following two puzzles are almost identical. The only difference consists in the words printed in boldface. The two solutions, however, turn out to be totally different. Variant ...
3
votes
4answers
2k views

10 friends play a number game

You and 9 friends are playing a game, is there a way to force a win, if so, how, if not, what is the most optimal strategy? Gameplay: Each player can have a turn, or if he/she wishes, 2 turns. Each ...
14
votes
3answers
1k views

Touching Matchsticks

You are asked to place matchsticks on a flat surface such that each matchstick end meets three others, and no matches cross. It is easy to achieve this for patterns that extend indefintely: The ...
16
votes
2answers
2k views

The hardest string of words to verbalise in english

To clear some confusion, this is just a riddle. I think maybe the size is whats intimidating some, but it can be solved as you would any other riddle. There are no new techniques used here. atop the ...
12
votes
2answers
1k views

How long can this list of numbers get?

One afternoon, you start writing some whole numbers on a (very large) sheet of paper. First you write a one-digit number, then a two-digit, and so on, with each number one digit longer than the last. ...
8
votes
2answers
3k views

Numbers in quadrants of a circle - help me solve it

I saw this puzzle and don't know how to solve it: The only pattern I saw is 3 + 8 = 11 , 2 + 9 = 11, 6 + 2 = 8 and 1 + 7 = 8 Are there other approaches I should consider?
2
votes
1answer
302 views

Memory Enhancement Through Numeric Imagery - What is the longest or best coherent sentence/paragraph/story you can make?

The guy who recited 20k numbers of pi by memory alone used a system where he converted numbers into consonants and then grouped words or sentences together to remember a huge amount of numbers. Here'...
3
votes
0answers
114 views

Magical election of novices in a monastery [duplicate]

In a monastery, there is a special rite to elect new novices. All candidates (we're talking of a huge number, so let's assume an infinite amount) gather together in one hall that gets locked, so that ...
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 ...
13
votes
3answers
820 views

Searching for a secret door

You have reached the final stage of a game show, and now face an endless row of doors labelled $\ldots,-3,-2,-1,0,1, 2, 3,\ldots$, going from minus infinity to plus infinity. Your goal is to detect a ...
5
votes
4answers
2k views

What is the minimum number of matchsticks that you can use to build expressions having the following results?

Instructions You have a bag containing infinite number of matchsticks all having the same cuboidal shape and size. Digits can be made using these matchsticks: $0$ takes 6 matchsticks $1$ takes 2 ...
3
votes
1answer
2k views

Pouring problem [duplicate]

You are in the possession of two bottles, one with a capacity of 7 litres and one with a capacity of 11 litres. Next to you is an infinitely large tub of water. You need to measure exactly 2 litres ...
8
votes
1answer
2k views

On what basis have I split the alphabet into 4 sets?

I have split the 26 letters of the alphabet into 4 sets. Here they are: Set 1: $F G J L N P Q R S Z$ Set 2: $A M T U V W Y$ Set 3: $B C D E K$ Set 4: $H I O X$ Can you determine on what basis have I ...
4
votes
7answers
804 views

An Exclusive Party

Your neighbour is hosting a party for a select group of people. . Hoping to get in, you hide in the front lawn and watch as guests begin to arrive. The first to walk up is a man, who says "Hi, I'm ...
11
votes
11answers
4k views

Longest sentence with each letter repeated n times

Inspiration: This question was inspired by Word sets with no repeating letters Rules: Sentences can be of any length. Every letter used in this sentence, must be used n times. n can be any number. ...
12
votes
6answers
7k views

Greatest Digital Clock Number, with a Twist!

7 segments make up a number, some visible, some invisible. Just like on a digital clock: 88:88 or 04:00: There are 2 vertical segments on both sides and 3 horizontal segments in the center. What's ...
5
votes
5answers
23k views

Word sets with no repeating letters

I know a set of six 4-letter words without repeating a letter (i.e. using 24 different letters). Here is an example: Are there sets of words with no repeated letters and having four 6-letter words? ...
5
votes
1answer
438 views

The Inspector and the Hit man

Inspector Crumblesniff thinks he is on the verge of arresting a notorious Mafia hit man, but he needs your help. First, after a raid on Sal's Pizzeria, he found an address book with these contents: ...
1
vote
2answers
210 views

need help with a math equation puzzle [closed]

I'm trying to create a math equasion puzzle using the numbers 3, 7, 20 and 40. I want to end with an answer of either 7 or 40. Is there any way this can be done? Thanks for the help
8
votes
4answers
2k views

Find the width of the river

You find yourself with a friend on a completely deserted (devoid of objects or people) and flat plane. The only thing of note is a wide river; you can just manage to see the other side of it. There is ...
53
votes
2answers
4k views

The needle in the network - find it!

We all know it can be difficult to find a needle in a haystack, but in this puzzle you have to Find the NEEDLE in the network! A bit more detailed: Somewhere in the network pictured above ...
4
votes
3answers
1k views

At the Parking Lot

Alice and Bob started working part-time parking lot attendants. Bob was managing a car when Alice arrived late on the first day at work. A: I'm sorry for being late. How many cars have come in? B: I ...
8
votes
4answers
5k views

What is the sitting arrangement ?(double row question)

Question: Eight people are sitting in two parallel rows containing four people each, in such a way that there is a equal distance between and adjacent persons. In row 1 , A,B,C,D are seated and all ...
10
votes
2answers
1k views

Four-by-four square

Consider the sixteen cells in a $4\times4$ square. Two (distinct) cells are neighbors, if they share a horizontal or vertical edge; note that every cell has two or three or four neighbors. Now each of ...
5
votes
3answers
3k views

Find the password of the man's PC

A man locked his personal computer with a password and wrote some phrases in the hint box kept in his room. One day, his wife tries to login in his absence using the hints which contained the ...
10
votes
2answers
860 views

Dissecting a square

You are asked to dissect an $N \times N$ square into polyomino pieces such that each piece shares portion of its boundary with exactly $D$ other pieces, and no piece has area exceeding $N$. This can ...
14
votes
1answer
1k views

How to ensure your logic puzzle has no loopholes?

Alright, say you've made this logic based puzzle, but when you post it, people find tons of loop holes, that obviously wasn't what you want! You didn't tag it with lateral-thinking or brainteaser! It'...
1
vote
4answers
1k views

How to share this cake? [closed]

You invite all your friends to a birthday party. Three of your friends came. At the party, you need to share your cake equally with everyone. The friends that came aren't your best friends, so you ...
16
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 ...
8
votes
1answer
727 views

Product and Sum, Variant 2a

My friends Peter and Sam are excellent mathematicians and always think strictly logical. Yesterday I told them: "I have secretly chosen two integers $x$ and $y$ with $1\le x\le y\le 9$. I have told ...
14
votes
2answers
3k views

Product and Sum

My fellow mathematicians Paul and Sam are very fond of mathematical puzzles. One day, I came up with the idea on mathematical puzzles while three of us having lunch together. I: Hey, guys. I am ...
16
votes
6answers
2k views

180 degree rotation matchstick equality

Several matchstick digits are still digits when rotated by 180 degrees: Note that 2 is rotated to 2. Thus, we can make a matchstick arithmetic expression which is valid when rotated 180 degrees. For ...
18
votes
2answers
1k views

One word: Bacon

Decrypt the hidden meaning in the picture below: Hint 1: Hint 2:
12
votes
2answers
1k views

Escaping a hungry lion you can't outrun

You are at the edge of an enormous circular arena. A hungry lion is eying you from the centre of this area. You are both capable of running at the same maximum speed, but constraint within the arena. ...
5
votes
4answers
2k views

pairs of anagrams where the two words sound and look very different

This is a question about pairs of anagrams capable of flavouring puzzles as memorable and surprising because the two words are so different. One of my favourite such pairs is chesty and scythe. These ...
14
votes
6answers
1k views

Finding Doctor No

James Bond is invited to a party with altogether $128$ participants (including Bond himself, the host, and the hostess). At the beginning of the party the host takes James Bond aside and asks him to ...
13
votes
2answers
915 views

Find smallest rectangle divided into figures so each figure has 5 neighbours

The following 3x4 rectangle can be cut into pieces along grid lines, so that each piece has exactly three neighbors: Problem: Find the smallest rectangle on the integer grid that can be cut into ...
6
votes
2answers
360 views

Signal-network: Create a network that guides 2 signals

This is a different 'connect the dots' puzzle. Your task is to connect the blue and yellow nodes in the map below with links such that the created network guides two signals emitted from the two ...
10
votes
1answer
512 views

What is God's Number for the Rubik's Picture Cube?

It's been well known for a few years now that every Rubik's Cube scramble can be solved in 20 moves. However, this is only for the case where the orientation of the centers is not taken into ...
25
votes
9answers
15k views

How to cut 12 in half and get 7

Here's a puzzle that a teacher told me today: How can you cut twelve in half and get seven? Hint (only if you're stumped): Another Hint

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