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19
votes
11answers
57k views

6 Tries to Guess a Number Between 1-100

After every time you guess, you're told if you're right, too high, or too low. Is there a strategy you can use to guarantee you'll get it on your 6th attempt (or lower)? I know a strategy to get it ...
33
votes
18answers
11k views

Use 2, 0, 1 and 8 to make 109

Assemble a formula using the numbers $2$, $0$, $1$, and $8$ in any order that equals 109. You may use the operations $x + y$, $x - y$, $x \times y$, $x \div y$, $x!$, $\sqrt{x}$, $\sqrt[\leftroot{-2}\...
32
votes
3answers
5k views

Maximum time for ants to fall off stick

Suppose there are $n$ ants on a stick which has length 1. At any time, the ants may be facing left or right, the initial directions of the ants are arbitrary. Each ant can be modeled as a point in the ...
24
votes
4answers
7k views

Variation of 100 prisoners light problem

There is a classic problem below for which Dr. Yisong Song wrote a very well written and thought out series of solutions. The variation here I've never seen anywhere but am curious. I want to work it ...
15
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 ...
11
votes
6answers
12k 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 ...
22
votes
3answers
17k views

Write twenty-four from four numbers

Write 24 using the four numbers 1, 3, 4, 6 and basic arithmetic. Explanations: The given are numbers, not digits, so you can't group them using decimal notation. For example, you can't create the ...
20
votes
4answers
3k views

Checkerboard Infection

There is a dangerous bacteria, Checkerichia Coli, (or C. Coli for short) which lives in the squares of checkerboards. Squares with this bacteria living in their digestive systems are said to have &...
17
votes
3answers
3k views

Sink the Submarine

There is submarine somewhere on the number line. Initially (say, at midnight), it is at position $A$, and is moving $B$ units per hour to the right, where $A$ and $B$ are both integers; both $A$ and $...
14
votes
11answers
23k views

Mensa online IQ test question - big and small squares on a horizontal line

Doing the Mensa online IQ test at http://test.mensa.no/, I was puzzled by this exercise. I understand that asking for answers like this kind of defeats the entire purpose of the test, but it's stuck ...
10
votes
1answer
2k views

20 coins on the table

Two boys , Brian and Gabe, decide to play a game. They lay 20 coins on the table. Each player took turns taking 1, 2, or 3 coins. Whoever took the last coin won. Brian thought if he went first, he'd ...
14
votes
2answers
3k views

10 prisoners and 10 lists of numbers [duplicate]

10 prisoners are held captive by a cruel warden. One day he gathers them in the prison hall and tells them about a new game he wants to play: "Tomorrow, I will assign each one of you a random ...
13
votes
2answers
1k views

Horses and Tracks

I have seen this question before and I am intrigued that there might be various ways it can be solved. I do know of one way, but I am trying to find out if there is any other approach possible. The ...
11
votes
1answer
507 views

Twelve Labours - #07 Cleats 'N' Balls

This puzzle is part of the ‘Twelve Labours’ series, but can be solved independently. Previous instalments can be found here: Prologue | 01 | 02 | 03 | 04 | 05 | 06 Emerging from the barbers with a ...
15
votes
1answer
4k views

The seven piece silver chain

You have to stay for 7 days in a hotel outside your city. But you forgot to bring your credit card and are out of cash. You have a silver chain with 7 links. The rule in this hotel is that residents ...
9
votes
1answer
927 views

A new word puzzle

Here is a new, original puzzle that I have made! You have to find the word that I describe. Me, I am an introduction My anagram is past tense of what you are doing now. The homophone of my anagram is ...
7
votes
1answer
246 views

Four Directions #2 - Where and what am I?

To the North is a place you could wear on your feet To the South is a place that could mean alone To the West they play a ba' game in the street To the East is where Hallvard sits on his throne I've ...
6
votes
7answers
7k views

Help understanding the solution to a “shooting puzzle”

I need help understanding the solution to the following puzzle: Puzzle: There is a "triangular" duel between the three shooters. Everyone shoots one by one, can shoot once and any person he wants. ...
3
votes
1answer
186 views

Four Directions #3 - Where and what am I?

To the North, a mule may serve you in copper. To the South, you may end up rich or a pauper. To the West, "Keep it Weird" you may hear them mutter. To the East, if you visit, bring plenty of butter. ...
14
votes
2answers
565 views

Tiling rectangles with W pentomino plus rectangles

Inspired by Polyomino Z pentomino and rectangle packing into rectangle Also in this series: Tiling rectangles with F pentomino plus rectangles Tiling rectangles with N pentomino plus rectangles ...
13
votes
1answer
305 views

Piece de Resistance - Seven Images Are Worth Digits

Seven Images Are Worth Digits This puzzle is part of the "Piece de Resistance" series. Go back to Part 1 (Ace) for the story.Ace Two Three Four Five Six Seven ... Another colourful piece of ...
10
votes
3answers
920 views

See me once, See me Twice #7

Here I am again, with another See me once riddle. Have fun! See me once, at the start of the week See me twice, the men becoming bleak See me once, when gambling on chinese ground See me twice, saved ...
9
votes
4answers
1k views

What is the solution?

What is a word made up of 4 letters, yet is also made up of 3, Sometimes is written with 9 letters, and then with 4, Rarely consists of 6, and never is written with 5 ?
8
votes
2answers
259 views

Tiling rectangles with T pentomino plus rectangles

Inspired by Polyomino Z pentomino and rectangle packing into rectangle Also in this series: Tiling rectangles with F pentomino plus rectangles Tiling rectangles with N pentomino plus rectangles ...
7
votes
6answers
544 views

Tiling rectangles with N pentomino plus rectangles

Inspired by Polyomino Z pentomino and rectangle packing into rectangle Also in this series: Tiling rectangles with F pentomino plus rectangles Tiling rectangles with T pentomino plus rectangles ...
6
votes
2answers
262 views

Tiling rectangles with V pentomino plus rectangles

Inspired by Polyomino Z pentomino and rectangle packing into rectangle Also in this series: Tiling rectangles with F pentomino plus rectangles Tiling rectangles with N pentomino plus rectangles ...
5
votes
4answers
536 views

I make billions (#3)

I make billions (#3) My products are quite edgy, But most have been a bust, I'm only one of many, Lord knows who we can trust, I'm not a politician, Yet I work with presidents, ...
4
votes
5answers
38k views

What color was the bear [duplicate]

This is an old one but I don't see it here. A man stepped out of his tent with his rifle and walked 1 mile south, 1 mile east and 1 Mile north. Then he shot a bear in front of his tent. What ...
4
votes
2answers
2k views

A modified version of apples and oranges logic

Question: You have 3 baskets, one with apples, one with oranges and one with both apples and oranges mixed. Each basket is closed and is labeled with ‘Apples’, ‘Oranges’ and ‘Apples and Oranges’. ...
4
votes
2answers
280 views

Find the value of $\bigstar$: Puzzle 5 - Every little Symbol

This puzzle replaces all numbers (and operations) with other symbols. Your job, as the title suggests, is to find what value fits in the place of $\bigstar$. All symbols abide to the following rules:...
3
votes
3answers
215 views

Tiling rectangles with U pentomino plus rectangles

Inspired by Polyomino Z pentomino and rectangle packing into rectangle Also in this series: Tiling rectangles with F pentomino plus rectangles Tiling rectangles with N pentomino plus rectangles ...
3
votes
3answers
1k views

A boy and his father [closed]

A young boy is taking a ride with his dad when a truck runs them off the road, killing the father and critically injuring the young boy. He's Medivac'd to the nearest hospital as the child is lying on ...
246
votes
6answers
21k views

You have prepared. You are determined. You approach the door

Hints:
134
votes
8answers
37k views

How can 64 = 65?

Here is a interesting picture with two arrangements of four shapes. How can they make a different area with the same shapes?
107
votes
9answers
15k views

A hunt for long forgotten treasure …but beware the pirate's curse!

I never really knew my uncle growing up. He seemed nice enough, but I got the sense from the distant, troubled look in his eyes that there was at least some truth to the rumours... Years before I was ...
68
votes
9answers
493k views

Crack the lock code

Does any one know how to crack this? I got this as a challenge.
139
votes
2answers
9k views

A mysterious email from Andrew Void

You are a secret agent in the service of the KGB, about to embark on a highly dangerous mission to infiltrate MI6. You have your disguise, your papers, and your backstory all prepared. The night ...
24
votes
3answers
3k views

I can be 22 intrinsically and have a possible range between 22 and 96 (44 at the start)

I can be formed in many ways, and four parts are always involved. Sometimes the formation can happen with all four parts at once, but sometimes some parts come later than the others. The highest ...
55
votes
8answers
5k views

Find a straight tunnel

There is a circular area with radius 1 km. And there is a tunnel, which is just under the surface, but invisible - unless you dig. It is known that the tunnel goes under the area (at least touches it ...
46
votes
12answers
10k views

Challenge for lovers

One of my friends gave me this puzzle. Please help me find the answer for it. Jane and Mike have fallen in love, and Mike wishes to send her a ring via mail. Unfortunately they live in Kleptopia ...
37
votes
3answers
4k views

How do I write a “solid” Riddle?

This is about the objective interpretations/assessment/quantification of riddles. Let us define a riddle as a type of puzzle relying on the usage of only language and context. Using precise English ...
33
votes
12answers
10k views

Unexpected hanging paradox

The unexpected hanging paradox is as follows: A judge tells a condemned prisoner that he will be hanged at noon on one weekday in the following week but that the execution will be a surprise to ...
22
votes
12answers
157k views

Four prisoners wearing black and white hats

There are four prisoners. All four prisoners will be freed, if at least one of them correctly guesses the color of the hat on his head. They can't speak to each other, and they can't touch each other....
32
votes
13answers
7k views

You will have to pray!

This riddle is so easy that I already have created another one. Just in case. Anyway, please avoid wild guesses. For sure I am queer and out of place Are you still here? Go start the chase But ...
15
votes
1answer
1k views

One beer too many

You're standing outside your apartment building after a late night out, with perhaps one beer too many, and you realize you have completely forgotten the code to get in. Luckily, you're a mathematical ...
25
votes
9answers
17k 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
11
votes
6answers
7k views

Who has mud on their forehead?

This is probably my favorite puzzle. It uses logic, but it's not one of those "logic table" puzzles which i dislike immensely. What is this type of puzzle called and are there more like it ...
64
votes
3answers
3k views

Riddled and Dismembered

The following is a riddle. Do not solve the riddle. Instead, explain the title. My top is tilted to the light, A trumpet, almost, in its form You court a woman? There I am. I please, palliate,...
57
votes
3answers
6k views

What is a Shy Word™?

This is in the spirit of the What is a Word/Phrase™ series started by JLee with a special brand of Phrase™ and Word™ puzzles. If a word conforms to a special rule, I call it a Shy Word™. Use the ...
35
votes
12answers
9k views

The total cost of salaries in a company

Story Version (scroll for TL;DR) It's the end of the first quarter of 2017. This means it's the end of the 2016 fiscal year (at least in my country it is). It's time to draw the line. So the CEO did ...

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