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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
4answers
244 views

Weighing Counterfeit coins

There are $n=4$ coins and we know exactly $2$ of them are counterfeit. In $2$ weighings, how can we find which of the four coins are the counterfeit ones? Assumptions: the counterfeit coins look ...
-1
votes
2answers
125 views

How many mice will be eaten? [closed]

A cat and a half eats a mouse and a half for an hour and a half. How many mice will be eaten by 100 cats for 100 hours?
4
votes
1answer
134 views

An unambiguous number puzzle

One is four, two is six Three is one, four is one Five is nine, six is five Seven is nine, eight is nine Nine is two, ten is five Eleven is seven, twelve is eight. What is thirteen? Note: the ...
7
votes
3answers
198 views

A 4 x 4 Magic Square with Pairwise Relatively Prime Entries

Find a 4 x 4 magic square of positive integers such that any two of its entries are pairwise different and relatively prime, i.e., have no common divisor greater than 1. What is the least that the ...
1
vote
1answer
75 views

Meeting of 2 Drunk Walkers (Random Walk) [closed]

There are 2 drunk guys who walks according to a Random Walk. Each of them, with equal probability of $ 0.5 $ turns either right or left. They both start at the origin and their turns are synchronized ...
4
votes
8answers
545 views

Let's play tag!

I have a short and bitter-sweet riddle for the community this evening. As always, I hope you enjoy it; good luck! I want to play a game of tag; however, there are some very important rules: We both ...
1
vote
1answer
64 views

Leaps and Bounds [closed]

Cunning Coyote is in a race with Joe Jackrabbit. They both take the same size steps, but the coyote takes 14 steps in the time it takes the rabbit to take 9 steps. Cunning Coyote decided to let Joe ...
3
votes
2answers
172 views

Should I Rest at the Travelator or Not at the Travelator?

This is a real-life puzzle encountered by one of my friends, again. After landing and arriving at the airport, I want to pick my baggage up quickly. The problem is that the baggage claim is $500$ m ...
12
votes
5answers
476 views

Labelling a Snow Flake Graph to Attain Minimum Sum

Label the vertices (or nodes) of this graph with positive integers so that any two nodes are joined by a edge (or line) if and only if the corresponding integers have a common divisor greater than 1 (...
1
vote
0answers
73 views

Filling a sudoku/latin square like array

Let us build a square array in the following manner, which I would like to call a modified sudoku: 1) Every row and column contains only one copy of a positive entry and there are exactly $t$ such ...
2
votes
1answer
169 views

Find the missing numbers 1, 3, 6, ?, ?, ?, 45, 55

1, 3, 6, ?, ?, ?, 45, 55 I asked the person who gave this to me and they assured me that it's correct. After an hour, I've given up :(
9
votes
2answers
305 views

A weird number system (I made it myself)

So, I'm an eccentric mathematician. You can see this with my number system. I'm pulling a sneaky on you, and you'll have to tell me what everything means. I'm not telling you a thing: figure it for ...
0
votes
3answers
110 views

Paper bundle question [closed]

There is a paper bundle of 500 papers.The height of this paper bundle is 5cm.I took 1 paper from the paper bundle and folded it into 50 times then what is the height of that folded paper?
4
votes
2answers
225 views

A small set numerical puzzle

Three, Twenty-one, and forty-five start this list that has arrived. ---edit for a little more clarity--- Ninety-one and one hundred and twenty. Then we get to the doubly interesting number....
11
votes
2answers
272 views

Pucks in the arena

Two identical pucks of radius 10 cm are placed in a round arena of radius 1 m. They are positioned 50 cm away from the center of the arena on opposing sides. Assuming no energy losses during sliding ...
3
votes
3answers
272 views

left and right hand sides are different why?

Let's say I have 50 coins total. I give 20 coins to my friend I am left with 30 Then I give 15 again I am left with 15 Again I give 9 I am left with 6 Again I give 6 I am left with 0 ...
0
votes
0answers
106 views

hard Numerical sequence [duplicate]

I need help to figure out what values should be put instead of the ? that's the sequence: ?, 36, 36, 18, 16, 14, ? I've tried to find a pattern and the only thing that I could think of was a ...
-5
votes
1answer
51 views

Next number in the following sequence [closed]

1, 2, 3, 5, 8, 13, 21, and so on. Find the next digit.
16
votes
5answers
2k views

How much had really been ordered? [closed]

The clerk misunderstood the order for rope. He reversed feet and inches, and the customer got only 30% of what he ordered. How much rope had really been ordered?
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 ...
4
votes
2answers
191 views

Using only numbers 1,2,3,4,5,6,7,8,9,0 and addition,make up to the sum 100.using numbers only once?

Using only the numbers 1, 2, 3, 4, 5, 6, 7, 8, 9 and 0 With only addition can you make a sum of 100?
4
votes
3answers
847 views

Uncanny Addition

? ? + ? ----- ? Replace every question mark (?) in this addition with a single digit so that the addition is valid and ...
2
votes
0answers
95 views

ARG Puzzle Gate 15 Help

Me and my group (yes I'm in a group trying to solve this) are currently working on an ARG puzzle and we are stuck. The first image/clue to the entire puzzle is what is seen below. The creator of this ...
6
votes
3answers
143 views

Discrete Peaceful Encampments: Player 4 has entered the game!

Here's a variation of Discrete Peaceful Encampments: Player 3 has entered the game! (which itself is a variation of Peaceful Encampments). You have 3 white queens, 3 black queens, 3 red queens, and ...
3
votes
1answer
171 views

What is the next term of this sequence?

What is the next number? $$2,3,10,12,13,20,?$$
6
votes
5answers
249 views

Book Lenders Puzzle (Answer with the least amount of steps in 5 days wins!)

You are a Book lender who strangely lends books of equal length and difficulty ever time. You have people who you lend your books to, but you want to find out who is the fastest reader of the group ...
8
votes
1answer
1k views

Staying grounded

I found a somewhat meaningful sequence that is not on OEIS yet, incredible! Here are the first 100 numbers of this sequence: ...
3
votes
1answer
101 views

Find a specific path on an n x n grid [duplicate]

Given a puzzle of the following form: Find a path between the top left corner to the bottom right corner, visiting each spot (.) exactly once. You can only move horizontally or vertically. ...
5
votes
2answers
184 views

Rotating 12 players on 2 tables

I'm stuck trying to find a good way to rotate 12 poker players on 2 tables. Assumptions: There are 12 players There are 2 tables We play for 4 hours Playing with sb means sitting at the same table ...
14
votes
0answers
576 views

Peaceful Encampments

This math puzzle is due to Donald Knuth (as far as I know; maybe he got it from someone else) circa 2014. Consider a plain represented by the unit square. On this plain we want to “peacefully ...
7
votes
1answer
233 views

Unlucky thirteen

These two separate sequences use the same rule and stop at the 13th term. 2, 1, 8, 5, 2, 5, 8, 6, 7, 9, 7, 7, 0 3, 1, 5, 3, 9, 2, 4, 3, 9, 7, 3, 1, 0 These examples are produced when the ...
2
votes
1answer
165 views

need help in solving that numerical sequence

Sequence: 2, 3, ?, 8, 6, 7, 6, 5, 9, 3, ?, 1 I've tried to figure out what number I should replace to the *?*I have initially thought that was a modified fibonacci sequence example: we start with 2+3=...
7
votes
1answer
165 views

Three stubborn siblings

2560147913 Three stubborn siblings, of which only one is whole, making history is their goal. What word am I looking for?
1
vote
2answers
154 views

What is the secret of this Math(s) “joke”? [closed]

On a page called 14 jokes only intellectuals will really understand, it lists: A mathematician is heading to a house party. Just as he is coming up to the house, he notices there are no cars parked ...
9
votes
5answers
232 views

What's for dessert?

Another puzzle, yay! What do I want for dessert? An element, a blue liquid you breathe. The end of a sentence. wgpz tzggjr wgvxf bmzzi mzy It's three til' 4, plus forty more. Hint:
8
votes
8answers
1k views

What mysterious whole number am I?

From my second point of view I copy that amount of first. I am the dominant side of two but for many I'm the worst. I'll be tricky to find but today might be your day, after all my neighbour is 2/3 of ...
0
votes
1answer
166 views

Sequence solving

I need help to find the x: 6 3412 x 8605648 I've noticed that the end doubles everytime so we have 6 then 12, then we should have 24 then 48 , I have also noticed that the first 2 numbers ...
1
vote
1answer
170 views

Number sequence solving

Help me solving this sequence: need help 9,?,342,675,1230, ?,3561,5892 Source: http://zagaza.ru/za548.htm
5
votes
6answers
282 views

2019 to every day of the month

The grumpy professor looked at his class and said - ok so now it is 2019 can you use the four digits individually with *, +, -, /, ^ (raise to the power of) and ! to make each day of the month? You ...
13
votes
3answers
1k views

Spider and fly on a cube

A spider and a fly play a game with a cube of side length $s=1$ and with a positive real number $d$. First, the spider picks its starting point $S$ somewhere on the surface of the cube. Then the fly ...
0
votes
1answer
149 views

Solve this sequence -pattern

Ok,I need to find the solution to this sequence: 1.(09), 1.(4), 2, 3, ?, 17 the number in parentesis is an infinite decimal like 1,099999 or in the second one 1,4444444,but i can't find an answer for ...
7
votes
2answers
186 views

Which number goes in the square with the question mark?

My friend, who loves puzzles as much as me, gave me this image this afternoon. My friend game me a hint: Skyscraper, which, as Daniel Mathias pointed out in the comments, is a type of grid puzzle.
13
votes
2answers
712 views

Digit sums of successive integers

For a natural number $x$ both, the digit sum of $x$ and the digit sum of $x+1$ are multiples of $7$. What is the smallest possible $x$?
-2
votes
2answers
110 views

Make 'b' the subject in the quadratic formula [closed]

Solve for b in terms of a,x and c in the fastest way possible.
2
votes
2answers
360 views

Can the sum, difference and product of 2 numbers be perfect squares? [closed]

If we take 2 numbers $x$ and $y$ such that $x>y>0$ and , can $x + y$, $x - y$ and $xy$ all be perfect squares?
3
votes
2answers
78 views

Can you have the harmonic, geometric, arithmetic and quadratic mean of 2 numbers all being integers? [closed]

I created this problem looking at the hm-gm-am-qm inequality (hm = $\frac{2xy}{x + y}$, gm = $\sqrt{xy}$, am = $\frac{x + y}{2}$, qm = $\sqrt{\frac{x^2 + y^2}{2}}$ and hm $\le$ gm $\le$ am $\le$ qm). ...
10
votes
2answers
1k views

All neighbor sum is 0 on a chessboard

Neighbor cells of a matrix are defined as all the cells that share a common edge. A matrix is formed by putting real numbers in each cell. Form an $8 \times 8$ matrix (like a chessboard) where sum of ...
1
vote
2answers
100 views

Funny Business, Math Problem [closed]

The population of Humorville is 9,800 people. In this town, jokes travel fast. In one hour, each person who hears a joke tells three other people who have not heard it and tells no one else. Last ...
4
votes
1answer
208 views

This picture has some hidden message. What is it?

This picture was uploaded for the Olympiads of Medicine, from Porto. While the answer might be in portuguese, I don't find it likely. I tried some Caesar Cyphers, I assumed the colours represented ...
9
votes
1answer
308 views

The Lazy Laser Physicist: Part 2

The Lazy Laser Physicist is quite shocked about what happened to his setup over night: Almost all of his mirrors were taken away, but some other things have been put on his table. Besides these there ...