Questions tagged [mathematics]

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

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8
votes
6answers
2k views

How many scouts are there?

At camp every tent is given a number. My twin lives at the reverse of my tent number. The difference between our tent numbers ends in two. What are the lowest possible numbers of our tents? A problem ...
8
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4answers
517 views

Circle inside circle

Here's a fun little math problem I made(by fun I mean no complicated methods needed at all.) You have a large circle with radius N with a cross in it to seperate the 4 quadrants(so that the figure ...
12
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1answer
331 views

Crossword, but math!

This kind of puzzle is from my mom's puzzle magazines. There it is called Figure Logic. It is essentially a crossword, but with math. In crosswords, all words must be real words. In Figure Logic, no ...
3
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7answers
2k views

Make 28 with the numbers 2020

Try to make 28 from the numbers 2020. Allowed operations: +, -, x, ÷, ! (factorial), exponentiation, square root, squaring, parentheses.
15
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4answers
1k views

Random walking on a board

There’s a pawn starting in the center of this game board. At each move, it can advance randomly towards any of the adjacent squares sharing a common side with equal chance. What’s the probability of ...
6
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5answers
848 views

The Starks, Parks, Clarks and their kids

Inspired by Martin Gardner's puzzle from his book John,a new student at the Math Department of the College, was invited to a get-together at one of the Professor's house. Professor Stark welcomed ...
10
votes
2answers
211 views

The special machine

There is a machine, which when you put a number card which has written $x$ on it, it will output a number card with $$x^2+10x+20$$ on it. John has a number card on his hand, then repeated the ...
8
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2answers
3k views

Alice and Bob play a game

The rain was still falling and Alice and Bob were terribly bored of having to stay inside the caravan, so they decided to play a game. The game is that Alice chooses a number $x$ in the interval [1,n] ...
16
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1answer
900 views

What is the Color Code™?

Inspired from Can you name the country code? and What is a Number™? series $ \begin{gather} % custom template - reuse if you may \def\S#1#2{\Space{#1}{21px}{#2px}}\def\P#1{\V{#1em}}\def\V#1{\S{#1}{9}}...
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4answers
1k views

The enclosure on a grid

On an infinite 1 by 1 grid, we want to make an enclosure with 20 fences that are each 5 units long. The two ends of each fence has to be on a node of the grid. What is the maximal area of the ...
5
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5answers
2k views

Ants moving from A to B and back

I am trying quantitative aptitude questions of a qualifying exam and I couldn't solve this question. A stream of ants go from point A to point B and return to A along the same path. All the ants move ...
31
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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 ...
5
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1answer
212 views

What was Matt's matchstick puzzle?

Something rather funny happened at our Puzzlers' meet the other day. "Oh hey buddy, can you hand me exactly 18 matchsticks? I wanna show you this new matchstick puzzle I came up with." Matt ...
4
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1answer
280 views

The Game of Numbers (#01)

I've just started hanging out with my friend Agatha, but we don't know what do to. Suddenly, she comes up with an idea: A game of numbers. These are the rules: Pick a number between 7 and 100, ...
10
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5answers
760 views

Length of an integer is part of its digits [closed]

How many positive integers less than 1,000,000,000 contain their length as part of their digit string? Example: 123466 has a length of 6 and 6 is one of its digits. Hence this number needs to be ...
4
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3answers
339 views

Scientifically Themed Rebus/Dingbats - Part 3

The same idea as before: the "scientific" expressions represent some form of popular media. Enjoy. Part 1 Part 2
12
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1answer
1k views

222 x 555 = hill

When I multiply numbers that contain twos and fives, I get a number, the digits in which first increase and then decrease, for example: ...
1
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1answer
90 views

A question based on cutting a wire to form a tetrahedron

I am trying exercises of Quantitative Aptitude and I am unable to work out how this problem can be solved: As a tetrahedron has 6 edges, I thought 5 cuts should be required. But that's wrong. Answer ...
13
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2answers
2k views

A puzzle question asked in mathematics exam

I am self studying for an exam and I am unable to solve this quiz question. I tried to find the numbers in the sentences but I couldn't find them and I think that's a wrong approach. Can anyone ...
7
votes
1answer
878 views

Unable to solve a question asking to find the missing number in sequence

I am trying some quantitative aptitude questions and I am unable to solve this particular question: Unfortunately, I have no clue how it can be solved; I am not able to start. However, I know the ...
6
votes
1answer
229 views

Question which is sort of puzzle from mathematics Exam

I am self studying and trying questions of quantitative aptitude in my mathematics exam and I am unable to solve this problem. Of three persons $A$, $B$ and $C$, one always lies while the others ...
14
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1answer
612 views

The numbers on blackboard

The numbers $2020,2019,2018,...,1$ are written on the blackboard from left to right. John repeats the following process until there is only one number left: John chooses the first two numbers from ...
0
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1answer
254 views

Math tapestry puzzle #3

Continuation from Math tapestry puzzle #2 Now things are heating up, it looks like this is slowly becoming bigger. I saw my friend Anna working on her tapestry. She asks me, "Do you like it?"...
5
votes
2answers
179 views

Swapping the first and last digits of an integer

Take any n-digit integer (n > 1) and interchange its first and last digits. If neither of these is 0, and they are different, does it happen infinitely often that the resulting number is a multiple ...
4
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1answer
254 views

What is the maximum length of sequence where the sum of 5 consecutive numbers in positive and sum of 8 consecutive numbers is negatve

What can be maximum length of such sequence? Hint one such sequence is
3
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1answer
99 views

Find the unique passcode

"Is this the Coldport Lost Property Office? I think I left my puzzle-book on the train this morning, and I was hoping someone had handed it in." The speaker was a tall gentleman with a six-...
5
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4answers
360 views

Complete this cross sequence

What is the next element of this sequence and why? Possible choices: Hint 1 Hint 2 Hint 3 Hint 4 Hint 5
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2answers
166 views

Missing number in a set of four segment circles

This is a puzzle posted on a social networking site that I have been trying hard since yesterday to solve: My approach has been to find out a mathematical function with the numbers in the yellow, ...
3
votes
1answer
205 views

Is this Series limited to six numbers only?

May be this problem is already answered. I am not aware. What is the next number in the following series? Importantly, after that number, are there any more numbers? is there a math related reason for ...
7
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2answers
626 views

Lock Optimisation

In a simple combination lock, a sequence of several digits is used as a password, with one wheel per digit. Generally, it is not possible to unlock the lock without knowing the password, but due to ...
14
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3answers
318 views

Cryptic Crossword?

You pick up a discarded newspaper, hoping to satiate your need for puzzles with a cryptic crossword. But as you turn to the page, you feel something is awry – perhaps some elision? Across 3. $F_6,F_7,...
21
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4answers
2k views

Boys and girls in a circle

There are $28$ students in a class, and each of them are either boy or girl. They sit in a circle, and claim that “The two people next to me are of different gender than each other.” It's known that ...
2
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1answer
101 views

Calculation puzzle 006

Find the number which corresponds to the place indicated by the question mark. ...
3
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3answers
120 views

finding a number using clues [closed]

The digit on hundreds place of a three-digit number is 2, the digit on tens place is 3 less than the digit on ones place. 6 times the product of the three digits is 20 less than this number. What is ...
3
votes
2answers
226 views

Cannonballs packing

A pile of cannonballs stacked like a pyramid has a rectangular base. Each layer has a length and a width in terms of cannonballs that are each one less than those of the layer that is directly below. ...
6
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1answer
306 views

Scientifically Themed Rebus/Dingbat Puzzles - Part 2

below are more rebuses with "scientific" expressions that represent something in popular media. Part 1 here. One of the questions in Part 1 has a link to a question here.
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3answers
2k views

Knights on a Torus

An 8×8 chessboard is in the shape of a torus. (This means that the board "wraps around" - you can go left from a2 and come out on h2, for instance. It also works vertically - you can go up from f8 and ...
8
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4answers
821 views

Scientifically Themed Rebus/Dingbat Puzzles

Below I have created a list of a few "scientific" expressions that represent some form of popular media, with the type stated. Hope you enjoy.
6
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2answers
782 views

Exam statistics

250 teenagers gather for an exam. Peeking at the roll, a math-inclined among them note that if they are split into 10 groups of 25 per alphabetical order, then in each group, there are two with the ...
10
votes
3answers
259 views

Find a good strategy to survive the multiplayer duel

Alice is involved in a duel with $N$ other opponents. She can choose a gun for herself with any hit probability as she wishes. She also prepares guns for her opponents, whose hit probabilities she can ...
3
votes
1answer
175 views

Calculation puzzle 005

396 ? 556 99 872 664 I tried to solve it but to no avail. Possible answers are 666, 491, 654, 999 and 917; since, the exam was multiple choice we were ...
20
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3answers
2k views

1 in, 1 out (The Security to the Party Maze)

A party is being held at a local mansion. The host is very rich and his success is because of one thing ~ his famous recipe for spaghetti! The spaghetti recipe is kept in a secret room inside the ...
5
votes
2answers
265 views

What should you substitute?

Find all functions $f:\mathbb{R}\rightarrow\mathbb{R}$ such that $$xf(x)-yf(y)=(x-y)f(x+y)$$ for all $x,y\in\mathbb{R}$. Problem by me. Most elegant solution gets the checkmark!
3
votes
1answer
211 views

Find the equation of this surface - The Snowman

Here is a surface that resembles a snowman: Its equation has the form $f(x,y,z)=0$: if a point $(x,y,z)$ satisfies that equations it is shaded, otherwise it is "left blank". Your goal is to find $f$. ...
3
votes
2answers
264 views

Fibonacci progression

In a number sequence, 1, 13, 169 and 2014 are respectively the first four terms of the sequence. The next terms are equal to the sum of the four numbers that precede them. For example, the fifth term ...
25
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1answer
827 views

An Evolutionary Experiment

Dr. Farnsworth entered class today and announced that we were going to conduct an experiment to see if we could force cells to evolve to communicate with us. The experiment is as follows: we are given ...
12
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5answers
2k views

Maximise your gold!

You met a genie. He gets $150$ magic lamps out, which are numbered from $1$ to $150$. You have to colour each lamp red or blue. After colouring, the genie will count the number of triples $T$ of magic ...
13
votes
8answers
2k views

n(n+1) as a multiple of 100

Here's a puzzle I came up with while walking today: For how many natural numbers $n$ is the number $n(n+1)$ a multiple of $100$? This is true for infinitely many $n$, so "how many" means something ...
10
votes
3answers
3k views

Lottery strategy

In a city, the official lottery consists of scratch cards that cost 10 bucks each. Each scratch card contains 36 squares with a hidden number on each square : 21 of them are “zeroes”, 9 of them are “...
14
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2answers
599 views

Sort 9 train cars on 3 paths

On the three paths of a station are A, B, and C types of train cars as shown in the figure. A locomotive driver (L) can attach from 1 to 9 train cars to a locomotive at any time, move them to the ...

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