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Questions tagged [mathematics]

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.

4
votes
1answer
209 views

Numbers Brain Teaser

I've come across a strange brain teaser on one of those sheets with things like: (man overboard) So here's the puzzle: 0 - 20 10 - 3 14 - 29 96 - 72 1977 I've been trying to ...
-8
votes
7answers
28k views

Make 24 With 7,3,7,3

You may use math signs you wish, but you must use the numbers 7,3,7,3 in an equation so it equals 24 Is it possible? If so, show how. No-nos: You are not allowed to combine numbers to make ...
3
votes
2answers
577 views

Bridge building with irregular planks

Imagine you have a big rectangular pond in your back garden. You wish to build a bridge from your house in the lower left corner to the small pagoda in the top right. You have lots of planks of ...
4
votes
2answers
247 views

How to make 18 from 1, 3, 4, 8

This question was on my sister's 5th-grade homework, practicing order of operations. It was to make 18, using the numbers 1, 3, 4, 8 and the operations +, -, and *. The instructions imply using each ...
7
votes
3answers
631 views

Homeostasis logic/math problem

I'm trying to derive a generic formula for a programming algorithm. I might be overthinking this or underthinking it... we'll see. Each of the triangles below represents a container. Each container ...
-4
votes
0answers
79 views

Discount Double-Check [on hold]

Fred needs to buy new sneakers. He has done a little research and has decided that the following three stores offered the best deals. Shoes For You is having a sale on all sneakers for 4/5 of the ...
8
votes
9answers
6k views

Why would five hundred and five be same as one?

Grandpa was in his crazy math mood again. "using rot13 and your math knowledge prove to me that 505 = 1" He said. Really? Can you? HINT
2
votes
1answer
6k views

Math Number Sequence Riddle with 4 numbers 8 digits [duplicate]

Create a number using only the digits 4,4,3,3,2,2,1 and 1. So it can only be eight digits. You have to make sure the ones are separated by one digit, the twos are separated by two digits, the threes ...
10
votes
1answer
359 views

Zero, One, Two, Three, etc

Find a solution to the following system of simultaneous equations. All letters stand for integers (positive, zero, or negative), and different letters are different integers. The preferred solution ...
6
votes
1answer
624 views

My friend is being a hypocrite

So I was having an argument with a friend and I know I'm right, but she just won't admit it and it's getting really irritating. She thinks this thing goes one way when it clearly actually goes down! ...
16
votes
7answers
5k views

These four numbers make 25

The sum of the whole is 25 Large and small are different by 4 The first is 2 times the fourth Third is equal to first What are the four numbers? This is really bugging me can not figure it ...
28
votes
3answers
3k views

Can you see out of the forest?

You are standing at the centre of a circular forest of radius 500 metres. The trees of this very regularly planted forest stand in a precise rectangular lattice on the plane, each 10 metres from the ...
11
votes
3answers
4k views

You surely don't want to score 100/100

The Story: Today, the Maths quizzes are handed out by the teacher. You got 100/100. Everyone got 100/100. But you're not happy with it. Everyone's not happy with it. You want to ...
12
votes
2answers
2k views

My Graph Theory Students

I have 18 students in my graph theory course this semester: Anne, Bernard, Clare, David,..., and Rachel. At the start of the course I asked them to draw the graph below, in which each of them is ...
11
votes
3answers
618 views

What's the combination for the safe?

The CFO sat back in his leather chair, which creaked and squeaked. "It's actually pleather," he said to the intern sitting nervously opposite him, a notepad resting on his knees. "We're very cost-...
28
votes
4answers
4k views

Happy pi day, everyone!

A baker is working a batch of dough. He shapes it into a cylinder of height a and radius z. What will the baker make from this volume of dough?
9
votes
1answer
157 views

What's the significance of this pattern?

Note, this is my first submission, let me know if I broke the rules. What is the significance of the following sequence of # signs? ...
32
votes
7answers
4k views

Who is our nearest planetary neighbor, on average?

Assume that the planets have circular orbits centered on the sun. Assume that the radius of the orbits is 0.39, 0.723, 1, and 1.524 for Mercury, Venus, Earth, and Mars. Assume also that there are no ...
3
votes
1answer
170 views

Albrecht Durer Inspired Magic Square

A magic square is an n-dimensional matrix in which each row, column, and main diagonal sums to the same 'magic number' (denoted by s). A normal magic square uses each of the numbers from 1 to n ...
6
votes
2answers
217 views

For what x can we solve $1,2,3,x=5$

This is a variation on the formation of numbers theme. Given $1, 2, 3, x$ in order, and the operations plus, minus, times, divide, and brackets, what single digits can x NOT be? i.e. find a ...
8
votes
4answers
2k views

Number of folds to form a cube, using a square paper?

Take a square paper of size S X S units, and thickness of paper 1 unit. How many half folds should we do to get form a cube out it? Consider infinite foldable paper.
3
votes
3answers
368 views

The Pebbles Quiz

We are in a TV game. We have 8 same looking boxes, each of which has 2 pebbles. Each pebble could be either precious or not precious. We choose a box and the host, without looking inside the box, ...
0
votes
1answer
122 views

How to solve this puzzling?

20190309,245111132328,331508165892,51222189610023,? A friend of mine gave me this number puzzling but I have no idea what is the logic. Does anyone know how to solve?
-3
votes
3answers
235 views

Only one option is correct [closed]

$a \in \mathbb{C}$ Which is the correct option: 1) $a = 1$ 2) $a = 42$ 3) $a = i =\sqrt{-1}$ 4) $0^a \in \mathbb{C}$ 5) $a^3 = 1$ Hint 1: Hint 2:
17
votes
2answers
447 views

Maximum Height of a Hotel with Strange Elevators

I encountered this puzzle many years ago, and I think back on it often as it is unique and thought provoking. As far as I know nobody has proved the given solution as optimum, so it may still be ...
5
votes
2answers
221 views

Geometry From Hell

You’re locked in a room with nothing but a pencil, a math compass, and paper. You do not have a straightedge. Your captors have informed you that you cannot leave until you construct (the endpoints of)...
4
votes
1answer
289 views

Chess Massacre Variants-Play Find The Fastest Way?

I have thought up several variations of massacre chess. Massacre chess is a game where almost every single move is a capture. The idea here is that only the chosen type of piece can capture. It ...
-2
votes
3answers
106 views

Get 2 liters from 4 and 5 liter buckets [duplicate]

You have a 4 liter bucket and a 5 liter bucket and an (infinite) supply of liquid. How do you get 2 liters?
5
votes
2answers
988 views

What's Bob's age again?

I created this problem myself, but I did have inspiration. Today is a special day, I'm moving out of my parent's house. My father comes to me and says "Wow, you're half my age. On the day we moved ...
1
vote
2answers
120 views

Cyrus' Adventure (Part 5)

Cyrus walked through the third door and went into a damp passageway. Suddenly, Cyrus found a big bug on the floor. "Damn!" Cyrus stepped on it and the bug died. After a while, Cyrus arrived at a small ...
12
votes
2answers
499 views

Waiting for the gravy at a dinner table

You are sitting at a round dinner table with $N$ other people (i.e. $N+1$ people all together). One of the other guests is the first to pick up the gravy boat and pour some on their potatoes. It then ...
6
votes
3answers
484 views

My Grandpa's Box #1

My grandpa died last month. At the reading of his will, he left me a strange wooden box. A post-it-note on the side read "You were always good at puzzles." There was a number lock on the front that ...
24
votes
4answers
10k views

The largest integer made of 1,2,3,4

What is the largest integer $A$ that can be produced from the four digits $1,2,3,4$ subject to the following rules? Each of the digits $1,2,3,4$ is used exactly once. Juxtaposition of digits is ...
8
votes
3answers
1k views

A first choice die

You and your friend have met to play a game of dice. This is a very simple game where both players roll a die at the same time, and the player with the lower score pays a coin to the other player. In ...
0
votes
2answers
110 views

Chess tournament winning streaks #2

So I asked a question here, which asks how many ways there are to score 7 points in 7 chess tournament games using the system on lichess.org, outlined both here and in the original question. That was ...
6
votes
2answers
484 views

I'm trying to create a magic square

I'm having trouble trying to make a $3\times3$ magic square with magic number $12$ and I can't figure it out. Can you please help me?
9
votes
1answer
577 views

Building a cheap road

The governor of Reniets (a land far, far away!) is known to be very stingy. He has to build a road which connects all the five cities in the region, which are oddly arranged on the vertices of a ...
4
votes
2answers
241 views

By American Standards

I once went to the USA and a guy asked me, "What is a+B?" I could answer him. What was my answer? HINT: Note: The title is appropriate, and B is capitalized on purpose.
6
votes
7answers
306 views

Find minimum number of meeting periods to reach 2 degrees of separation for a group [closed]

I am running a training course and I want to arrange a set of 1:1 meeting periods between the participants such that at the end of the day there is a maximum of 2 degrees of separation between any of ...
-1
votes
0answers
141 views

Help answering a puzzle

On a site, the Admin posted a puzzle and challenged users in chat to answer the puzzle. It has many of us stumped and without any real answers. I would appreciate any input on it or possibly the ...
9
votes
1answer
277 views

Chess tournament winning streaks

On lichess.org, they use a points system for keeping track of who is winning in a tournament. A win is worth two points, a draw is worth one point, and a loss worth zero points. Once a player has ...
24
votes
4answers
2k views

What is the most triangles you can make from a capital “H” and 3 straight lines?

So start with an upper case H, and then draw $3$ straight lines. What is the greatest number of closed triangles that you can form? For example: Note that triangles inside of triangles only count ...
29
votes
10answers
8k views

Using only 1s, make 29 with the minimum number of digits

Use the minimum number of ones to make 29. Here is the list of operations permitted: "Standard" operations, such as: $x+y$, $x-y$, $x\times y$, $x\div y$ Negation: $-x$ Exponentiation of two numbers:...
-5
votes
0answers
157 views

Numerical sequence help

I need help to solve this problem — I need to find the numbers that complete this sequence: 11, 89, 17, ?, 47, 62, ?, 10, 0 I have tried to solve it in many different ways but nothing came ...
14
votes
1answer
922 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 ...
11
votes
2answers
2k views

How should I approach using two 8s and two 3s to make the number 24?

Use two $8$s, two $3$s, and basic arithmetic operators ($ +, -, \times , \div$, parentheses) to make the number $24$. (You may not join numbers together to form new numbers, like $ 8, 3\...
-5
votes
2answers
104 views

Find the Smallest Value from these given digits [closed]

0 1 2 3 4 5 6 7 8 9 + - : x = Find the smallest value from these following numbers and equations. Each number and equations must be used once. You can make it like ...:(-1) Goodluck!
7
votes
3answers
438 views

Guess simultaneously, color of your hat, no passing allowed

1000 logicians standing in a circle are blindfolded and a hat of either black or white color is placed on each person's head. The blindfolds are then removed and each person can now see everybody's ...
9
votes
2answers
6k views

Crack the 5 digits code

I created this "crack the code" puzzle. I hope the members here like it.
1
vote
4answers
1k views

Birthdays on Consecutive Days

You are allowed to select as many random1 people as you like, and place them in a room. How many do you need for the probability that at least 2 people will have a birthday2...   a. on the ...