Stack Exchange Network

Stack Exchange network consists of 175 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

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.

3
votes
13answers
1k views

What is ls Largest Number Formed by only moving two sticks in 508?

Tilting the Image is not allowed. You can cannot change order of digits. You cannot change the Size if Digits unless you are harry potter. You can increase or decrease space between digits though. ...
3
votes
3answers
440 views

What are the fewest weights you need to balance any weight from a triangular seesaw?

I saw this question: What's the fewest weights you need to balance any weight from 1 to 40 pounds? Suppose you want to create a set of weights so that any object with an integer weight from ...
4
votes
5answers
2k views

Find 108 by using 3,4,6

Assemble a formula using the numbers $3$, $4$ and $6$ in any order to make 108. You may use the operations; $x + y$ $x - y$ $x \times y$ $x \div y$ $x!$ $\sqrt{x}$ $\sqrt[\leftroot{-2}\uproot{2}x]{...
30
votes
4answers
4k views
+100

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?
5
votes
3answers
531 views

Puzzling Equations

Mathematics is a fascinating field of study, ever changing, far from finished. Arbitrary symbols, prescribed with special meaning become extraordinary challenges for the mind. And if you’re like ...
16
votes
9answers
1k views

One-one communication

5 people are standing in a circle - person A needs to tell his salary to person B, but none of the others should know A's salary. How is this possible, if every person only whispers to the person on ...
0
votes
1answer
181 views

Fastest Way To 6 Pawns On the B To H Files

MASSIVE UPDATE: I decided to play around with this again today, and I found MAJOR improvmemts for the B to G file games. See if you can beat me! If not, give proof as to why my game is optimal (To ...
0
votes
2answers
83 views
0
votes
0answers
79 views
4
votes
2answers
179 views

100 prisoners' names in boxes, against smart warden

My question, which I do not know the answer to, concerns the classic 100 prisoners and 100 boxes puzzle, summarized below. The solution to this assumes the names are placed in boxes randomly, and gets ...
1
vote
2answers
278 views

The result is 7 game

The goal of this game is to find the lowest score for the 10 equations below. 0 ? 0 ? 0 ?...
1
vote
6answers
404 views

Product of Factorials

In the annual meeting of the International Conference of Puzzle Scenarios, each of $100$ people in a room is given a different number from the set $\{1!,2!,3!,...,99!,100!\}$. One person leaves the ...
0
votes
1answer
93 views

Arranging people in groups at a conference

54 people attend a conference. There are 6 tables that each seat 9 people. Each table has a different topic and all 54 people have to move around and sit at each table. Can you advise a formula as ...
-2
votes
1answer
171 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?
5
votes
2answers
137 views

Bracket schedule

my friends and I are doing beer Olympics. There are 12 teams with 6 games. Each game has its own “bracket”. Essentially there will be 6 winners, 1 from each bracket or game. Those teams will then ...
26
votes
9answers
8k views

A clock for 2017

Design a clock where each number from 1 to 12 is obtained as an arithmetical operation using each digit of 2017 exactly once: for example, 4 could be made as $2\times 7-10$.
41
votes
4answers
2k views

Hamlet and the theatre

Hamlet is preparing a play to find out the truth about his father's death. The theatre has $2015$ numbered seats and can contain all the members of King Claudius's court. He gives to each member a ...
44
votes
10answers
133k views

1 2 3 4 5 6 7 8 9 = 100

The sequence of numbers $1\ 2\ 3\ 4\ 5\ 6\ 7\ 8\ 9$ has the property that you can insert mathematical operators in between the numbers from $1$ to $9$ and make the expression evaluate to 100. For ...
-2
votes
2answers
140 views

All Unique Permutations [closed]

We have the word: RAPSEVNOBLURKANIWA We want to find the number of unique permutations that could be made with RAP always staying together, so that there are: no 3 adjacent consonants, ...
1
vote
1answer
272 views

Master and Slave versus Bob: hard version

Continuation of: "Sub-puzzle: Master and Slave versus Bob the Violent but Honest Psychopath" and "Master and Slave versus Bob: easy version" The hard version is identical to the easy version (see ...
1
vote
1answer
79 views

Find an infinite set of formula, take any $2$ they are SAT, take any $3$ they are UNSAT [closed]

Find an infinite set of (propositional logic) formula, $S$, which satisfies: If you take any $2$ elements from $S$, they are satisfiable. If you take any $3$ elements from $S$, they are unsatisfiable....
5
votes
4answers
318 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, ...
10
votes
2answers
698 views

You are almost there

I am, in a way, half of eight but not four - not that straight. I am, in a way, half of infinite my location is always definite. I can mean not only not positive for a logician but also almost or ...
2
votes
1answer
312 views

Distance from One

For random natural number $N_0 > 1$, we find $N_1$ by the rule: $N_{i+1} = \frac{N_i}{2}$ if $N_i$ is even $N_{i+1} = 3N_i + 1$ if $N_i$ is odd If $N_1$ isn't equal to $1$, we find $...
-3
votes
2answers
117 views

Arrange StakExchangePuzzling [closed]

Find the total number of permutations of the word STAKEXCHANGEPUZZLING such that the letters STAK always stay together. Rules: No 3 adjacent consonants, no 2 adjacent vowels. For every odd pair of ...
14
votes
2answers
360 views

Construct $\sqrt{3}$ using every natural number

Construct $\sqrt{3}$ using every natural number $n\in \mathbb{N}$ (1, 2, 3, 4...) exactly once and the operations addition ($+$) and division ($\div$).
7
votes
1answer
172 views

How many times does the earth rotate per year?

Assuming there are exactly $365$ days per year. How many rotations about its axis does the earth make in one year?
10
votes
9answers
7k 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
5
votes
5answers
831 views

How do I make numbers 50-100 using only the numbers 2, 0, 1, 9?

Rules Use ALL the digits in the year $2019$ (you may not use any other numbers except $2, 0, 1, 9$) to write mathematical expressions that give results for the numbers 50 to 100. You may use the ...
0
votes
0answers
91 views

Can you Solve it [duplicate]

----- + ----- + -----= 30 Use only (1,3,5,7,9,11,13,15)
61
votes
24answers
18k views

Make 0 0 0 0 = 8

Can you find a way to make: $0\ 0 \ 0 \ 0 = 8$ by adding any operations or symbols? You can use only these symbols: $+,\ -,\ *,\ !,\ /,\ \hat\, ,\ ()$. It is limited to this list, and ...
6
votes
5answers
945 views

20 cards facing down

You have a row of $20$ cards facing down. A 'move' consists of the following actions performed in sequence: Pick a face-down card and flip it face-up If there is one, also flip the next card on ...
32
votes
12answers
4k views

Mr. Hilbert and the Problem of the Erroneous Equation

Having had just checked into the Grand Hotel, Mr. Hilbert slumped into the hotel room armchair with relief. Finally he could have some peace and quiet and solve the quaint riddle his colleague gave ...
2
votes
0answers
71 views

I have a good question for thinkers out there. Mr. Mike's Retirement Party [duplicate]

When Mr.Mike finally retires, he is going to have a party on a cruise ship with all 12,184 of his former students. Each of the students will be given a number as they board the carrier. All his former ...
8
votes
1answer
423 views

A case of the sniffles

The cubicle farm at the Colla-R water treatment plant is laid out in a neat square: eight rows of eight cubicles with a narrow corridor between each cubicle (in the diagram the thin black lines are ...
9
votes
4answers
346 views

Not-Quite-Sufficiently-Advanced-Technology Square

This was given as an assignment to a group of sixth graders, who were told they could use calculators. Beyond that, no real assistance was provided. They were not working on it as a group, so ...
7
votes
1answer
300 views

Where did the mathematician go?

Two mathematicians were discussing their recent holdays. The first mathematician exclaims I was on an all inclusive trip to lanserote for two weeks. The second mathematician, slightly ashamed, ...
21
votes
6answers
2k views

A game with 52 cards

Alice and Bob play the following game with two (identical) standard decks of $52$ cards. First Alice secretly arranges one deck of $52$ cards in a long row on the table. All cards are face-down, and ...
8
votes
1answer
201 views

A Number Game puzzle

Our team has created 9 math puzzles with ranging difficulty. Let me share one of them. At the beginning a number is given to you. Your objective is to get a different number by making choices. Here's ...
6
votes
2answers
227 views

“Balls in Boxes in a Sack” Weighing Problem

This puzzle is based on a competitive programming problem in SG NOI 2019. Let's assume there are $100$ balls with some labels (e.g. with $100$ different marks on them) having different weights of ...
5
votes
1answer
262 views

Unlock my phone! March 2018

New month, new password, but I've already forgotten! Help! What is my phone's password this month? Hint #1: Hint #2:
14
votes
3answers
563 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 ...
34
votes
3answers
5k views

Do better than chance

You and an opponent are playing the following game: Your opponent picks two different real numbers, however he wants to, and writes them on two cards, which he presents to you face down You choose ...
5
votes
5answers
639 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, ...
2
votes
1answer
331 views

Guess the Function for Scatterplot of Number Theoretic Function

To my knowledge, this puzzle is not previously published (except by me on google+ recently), but I would be interested to hear of any info otherwise. This following graph was generated using a simple ...
11
votes
2answers
318 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)...
12
votes
1answer
466 views

Find the next number in this sequence

Find the next number in the sequence : 1; 5; 33; 25; 2; 16; 14; 12; 11; ? What is the next number and why ?
10
votes
1answer
1k views

Island of Liars

A king goes to an island, where there are 5823 people who always tell the truth and 8723 who always lie. The king is special guest for the party celebrating 2053 year. On the party, liars and ...
4
votes
1answer
239 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
29k 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 ...