Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

A puzzle strongly related to mathematical facts and objects, or whose solution needs serious mathematical arguments. General mathematics questions are off-topic but can be asked on Mathematics Stack Exchange.

3
votes
2answers
111 views

Numbered Billiard Balls

Ten billiard balls are stacked in the form of a regular tetrahedron, six in the bottom layer, three in the middle layer, and one in the top layer or cuspid. All the balls are numbered (with positive ...
0
votes
3answers
69 views

Guess Me riddle #3

View the last part here Guess the word Sir, I bear a rhyme excelling In mystic force and magic spelling Celestial sprites elucidate All my own striving can't relate What am I?
7
votes
1answer
116 views

A Christmas Tennis Tournament

Three friends, Charles, Hugh, and Freddy, played a one-month tennis tournament, just one match between two of them every single day during last December. During the tournament, whoever lost the day's ...
8
votes
4answers
477 views

Maxit negotiations

Your military junta has recently overthrown the government of Malta and taken control of the small island nation. As a way to finance your wise and just dictatorship, you have decided to threaten the ...
3
votes
2answers
154 views

This title is not a clue

$\color{#FFFFFF}{\textsf{I am required to have text in my question. This is not a clue. Stop reading and look at the image.}}$
4
votes
2answers
171 views

Input/Output Problem #7

See here for basic rules on problem. Input/Output Problem #1 Problem #7 Make an optimal machine that accepts sequences of integer digits 1-4 such that each triplet contains three different numbers. ...
3
votes
2answers
103 views

Input/Output Problem #6

See here for basic rules on problem. Input/Output Problem #1 Problem #6 Make an optimal machine that accepts sequences of integer digits 1-4 such that all 1s are at the beginning and all 4s are at ...
4
votes
3answers
152 views

Input/Output Problem #5

See here for basic rules on problem. Input/Output Problem #1 Problem #5 Make an optimal machine that accepts sequences of Rock Paper Scissors games where first input is Player 1 and second input is ...
4
votes
2answers
150 views

Input/Output Problem #4

See here for basic rules on problem. Input/Output Problem #1 Problem #4 Make an optimal machine that accepts sequences of digits 1-3 that contain a 1,2,3 in each triple of numbers and has no ...
3
votes
1answer
103 views

Input/Output Problem #3

See here for basic rules on problem. Input/Output Problem #1 Problem #3 Make a machine that accepts sequences of digits from 1-4 that have a product that is a square number.
5
votes
8answers
462 views

Input/Output Problem #2

See here for basic rules on problem. Input/Output Problem #1 Problem #2 Make an optimal machine that accepts any letter combination that begins with a consonant and alternates vowel consonant from ...
12
votes
3answers
814 views

Input/Output Problem #1

The basis for this problem is that you did to make an optimal pattern so that all inputted sequences will be "accepted" if they fit the rules of the problem and "rejected" if they break any of them. ...
0
votes
2answers
88 views

How many bulbs are switched on? [duplicate]

I remember this one from an interview: There is a room with 100 light bulbs (numbered from 1 to 100) lined up in a row. All the bulbs are off. 100 people are lined up in front of the room. The ...
-4
votes
0answers
65 views

Numbers Tricks in mathematics [closed]

The first digit of a four-digit number is the fourth digit of the four digits. Both the third and the same number. If the last two numbers are doubled to the first two numbers, the number of cars in ...
5
votes
4answers
229 views

Recursive Doors and Deluders Puzzle

You start off with $\$1.$ You are faced with $20$ doors, and in front of $10$ each are lying lookouts and honest guards. If you enter and completely walk through a door guarded by an honest hombre, ...
3
votes
0answers
118 views

Which Number Replaces the Question Mark?

Can you find out what the numbers below have in common? Can you figure out what comes next? ...
3
votes
2answers
305 views

Assets Split Puzzle

An old woman had the following assets: ...
1
vote
3answers
178 views

What is the 10-digit combination of Sherlock's locker?

Sherlock made an elaborate code to remember the 10-digit combination to his locker. This is the code he came up with: A-K-B-J-C-H-D-G-E-F Each letter stands for a single digit number (0-9) When two ...
3
votes
3answers
282 views

Grandpa's Numbers

Grandpa likes pencils but not pens Grandpa likes Beijing but not Tokyo Grandpa likes math but not chemistry Grandpa likes Contact but not _______ Make sure to explain! Hint 1: Hint 2:
1
vote
3answers
198 views

The evil genius infinite plan

I'm an evil genius and I'll conquer the world with my minions :] My minions have just 2 egdes but in just 2 minutes I've produced an infinite amount of them. You'll see how I will conquer the world- ...
4
votes
1answer
283 views

The triangle-sequence riddle

this is my number sequence: / - / - 1 - 2 - 7 - 6 - ? This riddle has somtething to do with equilateral triangles Good luck and have fun :) PS: please tell me if this is too broad, this is ...
8
votes
2answers
872 views

Mystery at the Arcade

7 people, A-G, were competing in the national championships of the new arcade game Corpse Deems Us. They each scored a whole number of points from 1 to 100 inclusive, but it wasn't clear what the ...
6
votes
2answers
2k views

100 Fruits for 100 Dollars a more challenging version

This is a more challenging version of the reported puzzle " How will you get 100 fruits in Rs. 100? " Bob buys 4 different fruits for exactly 100 dollars Jackfruits cost 15 dollars each ...
5
votes
5answers
378 views

Time-Motion puzzle

Time and Motion studies are well established. Here is an easy question: It takes 8 men 6 months to build 2 houses at a cost of $50,000. It takes 10 men 5 months to build 3 houses at a cost of ...
6
votes
1answer
337 views

I have a puzzle and a solution… it's the method I'm after

The cipher message is: J B A Z R X K Z N T W K O Y E Z The answer is: T O N G L A N D B R I D G E How did I (or more accurately my father) arrive at the answer?
13
votes
1answer
712 views

My Social Security Card Number

I have forgotten my social security card number. All I remember is that it is the largest integer with the property that the block of any two of its digits that are adjacent is either a two-digit ...
-6
votes
1answer
130 views

100 birds 100 rupies. parrot cost is 5rs, crow cost is 1rs and sparrow cost is 0.05paisa please solve this? [closed]

100 birds 100 rupees. parrot cost is 5 rs, crow cost is 1 rs and sparrow cost is 0.05 paisa. all 3 birds are required. please solve i want 100 birds on 100 rs.
9
votes
4answers
405 views

Cupcake division

A elementary school student brought cupcakes to their class to celebrate their birthday! However, there's a problem: There are 25 students in the classroom, and only 24 cupcakes! The students have ...
6
votes
2answers
454 views

I love baking, do you too?

I love programming, it's so fun Just get every computer in the world And just do program as much as you can Because with everyone on your side you can never go wrong with programming And no, ...
8
votes
4answers
959 views

A Mix of Puzzles

Weapon of the sea, undented, times x or y minus the first, reversed. 3-4 triangle complete. A bucky lemur nun. Shakespearean poem less nonagon's sides. Krypton minus vanadium. (omg ...
4
votes
3answers
193 views

Lots of children with Halloween candies

You are a teacher in a big kindergarden and halloween was just yesterday. You decided to put the children into a candy race by dividing them into 19 groups to gather candies from houses nearby (they ...
10
votes
3answers
974 views

Excited Raichu's Riley Riddle

Here's my first attempt at a Riley! Good luck! The thought of my prefix brings many a smile; Sit down, relax, or sleep for a while. My infix is, mathematically; One point six times ...
-4
votes
1answer
101 views

The unthinkable sequence

To correctly answer this question, I would like you to include the next 5 numbers of this sequence and also tell me why they are the correct numbers. 3, 4, 8, 9, 14, 23, 25, 31, 36, ?, ?, ?, ?, ? I ...
7
votes
3answers
217 views

Riley 007 by KrOmega

Just thought of a Riley, so I just posted it here (I've become obsessed with making Rileys lol) My prefix you say in astonishment, My infix within the prefix slightly smaller than a pie ...
6
votes
2answers
166 views

Number sequence solving strategies

Number sequences are one of the oldest puzzle categories in the book. You would find it hard to look through a days worth of puzzles posted here and to not find any puzzles that involve some sort of ...
9
votes
5answers
639 views

The Three Kings of Metsyssisab

In the world of Metsyssisab, there were three kingdoms, ruled by King Owt, King Eerht, and King Ruof. One day, a fourth, evil king, King Evif, who ruled a small island, looked to control all of the ...
26
votes
6answers
6k views

Noughty Mathematics Question

Use your imagination to follow these instructions: Take out an imaginary piece of paper. Turn it 90° clockwise. Make a mental note to use right-justification and nice, tight kerning and leading. In ...
0
votes
3answers
118 views

Smallest positive integer divisible by $1$ to $100$ [closed]

What is the smallest smallest positive integer $n$ such that $n$ is divisible by $1$ to $100$ and $n$ is not $0$?
-2
votes
1answer
77 views

Complete the sequence if a specific pattern is followed [closed]

1, 4, 9, 18, 35, _ Find the next number if the occurence of numbers follows a specific order
1
vote
0answers
86 views

Hard Questions About Circles and Polygons [closed]

a circle has 1500 chords draw in it so that the maximum number of non overlapping regions is obtained. find the difference between the number of points of intersection of the chords and the number of ...
3
votes
1answer
119 views

This four-by-four Magic Square uses all the integers from -7 to 8. Complete the square. More Magic Squares!

This four-by-four Magic Square uses all the integers from -7 to 8. Complete the square. This is what has been given so far: -7 _ _ _ _ -2 _ +1 _ _ +3 _ +5 _ _ _ Please Help. Thank you
9
votes
3answers
321 views

Special triangles in convex polygons

Given identical 30-60-90 triangles, what is the convex polygon with the highest number of sides that I can build from them? This seems a very easy task by first look, but I’m totally stuck right now. ...
14
votes
2answers
318 views

The Number Guessing Game

Two people are playing an interesting form of a number guessing game, with the following rules: One person is the guesser, and one person is the thinker. The thinker thinks of a number from 1 ...
5
votes
4answers
205 views

Coin Removal Variation

A variation on this problem, where coins can become neighbors. There is a line of $n$ coins on the table, all showing either heads or tails. The object of the puzzle is to remove all the coins by a ...
8
votes
1answer
770 views

Fill in the number. Not as straight as it looks

The square below is missing a number. You have four options 32 4 16 22 Please explain your answer HINT Something to do with addition
1
vote
1answer
69 views

Create a 3x3 Magic Square that uses integers from -10 to -2

I've never used this before but i'm having trouble with this. Create a 3x3 Magic Square that uses integers from -10 to -2. By the way, this is a weird magic square since diagonals don't need to ...
14
votes
9answers
7k views

Salesman's claim for mechanical keypad lock - 5 buttons and 545 combinations!

A company makes mechanical keypad locks. The keypad is a set of five buttons arranged vertically. O O O O O The buttons are quite close together. Once a ...
11
votes
3answers
2k views

Coin removal problem

I have a slight variation of the coin flipping problem. There is a line of $n$ coins on the table; some of them are heads up and the rest are tails up, in no particular order. The object of the ...
1
vote
2answers
117 views

5 subjects and their marks

The following partially-filled table shows the marks scored by 5 students named A, B, C, D and E in five different subjects, namely P, C, M, B and S. The marks scored by all students in all subjects ...
3
votes
1answer
83 views

Creating my climbing wall

[based on a true story] I have here some climbing holds that I've made. There are two relevant parameters: The angle on the top, and The thickness, as shown. Now it is definitely the case that $...