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.

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3answers
465 views

The first term of the 100th line? [closed]

In the following arrangement what would be the first number in 100th line? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
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3answers
120k views

The Jeweler and the Five Rings

A king asks a learned man to visit his palace, to which the learned man responds: "I will come some day next month, but I will not tell you on which day. Further, you must give me gold in grams equal ...
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2answers
119 views

How many are they, how much do you owe them? [closed]

Let's suppose you want to build a house. To do this, you're going to need people to help build the house. Specifically, you're going to need contractors, engineers, and construction workers. After ...
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3answers
407 views

Fast Mental Calculation of $7.5^7$ [closed]

I was recently asked the following question. Given $7^7$ and $8^7$, approximate $7.5^7$. My idea was that we know $(x + .5)^7, (x - .5)^7$ where $x = 7.5$. Then, taking their average would over ...
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3answers
135 views

Perkin's age problem [closed]

Perkin and Poise's combined age is 22 which is 3 years more than the combined age of Perkin and Pootle which is 2 years more than Poise's and Pootle's age combined. The question is - In how many ...
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1answer
703 views

Why does 12/2 = 7? [duplicate]

Here's a quickie while I work on the fourth floor of the Puzzle Dungeon. It's going to be here within the next two days, probably. Find a way to divide 12 by 2 so you get 7. There are several rules: ...
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1answer
90 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
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2answers
944 views

What is the minimum number of line segments that need to be made to cross all points on a $n \times m$ grid?

Given a grid of $n \times m$ points, on a sheet of paper, what's the minimum amount of lines (which can extend infinitely) required to pass through each point, that you can draw without lifting a ...
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2answers
199 views

Shifting the stack as it is

There are $3$ saucers. And there are $5$ disks, say A,B,C,D,E, having respective areas $1,2,3,4,5$. That is, E is the largest disk and A is the smallest one. They are placed in the order E,D,C,B,A in ...
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2answers
509 views

Binary manipulation game

I made a (for now, 2 player) game once that deals with manipulating binary numbers on a single list. Here are the rules. Rules For now, take $n=5$. If possible, provide a solution for generalized $n$...
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2answers
179 views

I need a solution for this puzzle [closed]

This is meant to be a simple puzzle Given that: 3 - 4= -1 5 + 3= 7 2 + 6= 15 30 / 6= 20 Find: 20% of the sum for the final answer Hint: Final Answer Format: 00/0=0 (/ = ÷) (Divide Symbol)
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1answer
200 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?
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2answers
74 views

Schedule of a business [closed]

With a group of 8 students you have set up a small business with which you help a customer every day during the holidays to clean up his computer and to redecorate it. For the next day there are 12 ...
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1answer
196 views

What is the next number in the integer sequence?

What is the next number in the following sequence? 25 27 30 34 39 45 52 60 69 79 69 60 52 45 39 34 30 26 22 18 82 78 74 70 66 67 64 60 65 80 ?
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2answers
185 views

Doubles and Trebles [closed]

There are two ponds having lotus flowers - pond A and pond B. The property of the flowers of pond A is such that they get doubled (that is twice) in number every day as compared to previous day (6:00 ...
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1answer
404 views

Deduce the numbers (addition + subtraction)

Two mathematicians are passing an exam, where the examiner informs them that he has chosen two different numbers between 2 and 100, such that one is divisible by the other. The examiner then tells the ...
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1answer
156 views

What is next: 2, 3, 5, 13, 89, 233, …? [closed]

Based on what is shown, what is the next number in the sequence?
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1answer
557 views

Measuring 4.6 liters with a 4.3L bucket and a 4.7L bucket

You are standing next to an unlimited source of water (the tap in your kitchen). You need precisely 4.6 litres of water. Luckily you found two empty buckets. One can hold 4.3 and the other 4.7 litres ...
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votes
2answers
202 views

It rains in Gadyukino

It rains in Gadyukino village every other day on average. Assume the probability of rain on any given day is 50% and independent. A local weather forecaster has the sole duty every day of predicting ...
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1answer
267 views

There's an ARG I've been working on, and I'm stuck on this puzzle part II

Hees the first one incase you havent seen it. There's an ARG I've been working on, and I'm stuck on this puzzle So from that we got our password for this "problem" however we havent ...
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1answer
301 views

The Programmers Bot!

Dr. Probot is a famous inventor, known for many creations, his most recent being "Bot". Bot is the very first working robot, he has 3 very basic instructions: Left Right Self Destruct Left: Rotate ...
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2answers
206 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.
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1answer
172 views

Integers, integers and integers? [closed]

Area of a rectangle having its length and breadth expressed as integers gets increased by 103% when its sides are increased by x% (say of length) and y% (say of breadth), where x and y are two ...
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1answer
86 views

Distance between two friends [closed]

Two friends are 200 meters apart in a concourse. They then both walk 100 meters each with their faces towards to each other. Yet after this 100 meter walk they are still 200 meters apart.
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1answer
148 views

How do I make numbers 0-100 using only the numbers 2, 0, 0, 4 in order? [closed]

Please help me I need to find out how to do this with maths.
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2answers
149 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, ...
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1answer
184 views

A quick mini brain teaser [closed]

For x positive integers, function f(x) which remains a mystery and nobody knows can be divided by all of the following five EXCEPT one number. 1, 2, 3, 4 and 6. Can you figure out which number cannot ...
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1answer
144 views

How old is this cat [closed]

If the mother's age was 2, and if the grandfather's age is 6, and if the father's age is the grandfather's minus the mother's + 1, And the cat's age is the father's age - the mother's age, how old is ...
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2answers
230 views

Solve XAB + YZCD = ZEXY

Replace each letter with a digit between 1 and 8 to make the equation $XAB + YZCD = ZEXY$ true. Each letter represents a different digit. Bonus question: How many solutions are there in total?
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4answers
401 views

Find pattern of number circulation [duplicate]

Question 1 => what is the pattern of this image? Question 2 => what is the source to become 42 at last?
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1answer
2k views

Calculating row number and column number [closed]

What I am trying to do is calculate the row and column of which an id is in. For example I have the grid 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 As you ...
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1answer
143 views

This weighs heavily on my mind [duplicate]

I have 9 coins that look identical, but one is heavier than the others. I want to identify that one. My brother has an old-fashioned balance scale that I can use, but I'll have to do annoying chores ...
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1answer
302 views

Mathematical Puzzle

1 * 1 = 1 2 * 13 = 2 3 * 3 = 3 44 * 8 = 4 73 * 5 = 0 90 * 60 = 0 Q1) What is the smallest set of numbers under this operation that can equal 5? 6? Q2) What is 8 * 9? Hint:
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2answers
739 views

Bridge's riddle [duplicate]

You're in a group of people going for an internship in a remote mountain lab. By mistake you pulled a lever with a skull just out of curiosity and it released some zombies. So you and your group had ...
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2answers
155 views

Walking around in circles [closed]

Imagine you are an ant walking on a circle. You start your journey from the blue point. Your progress is given in percentages - 100% being a full round trip. In the figure, you've made a progress of ...
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1answer
255 views

Calculate RPM ratio A to D? [closed]

According to the picture: cogwheels A and D have 60 jags each, cogwheel B has 40 jags, and cogwheel C has 20 jags. If cogwheel B turns at 20 RPM, calculate the ratio of A's speed in RPM to D's.
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1answer
711 views

Find the Different Sugar Cubes [duplicate]

There are 10 Boxes, each contains 1000 sugar cubes. The sugar cubes in 9 of the boxes are 10 grams each and the other box has 9 gram cubes. There is a digital scale that you can use it ONCE. (i.e. ...
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1answer
62 views

Number Sequence Puzzles : Find missing number in triangle [on hold]

Solve this question plz send me answer
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3answers
117 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?
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1answer
960 views

What is the correct solution to 16/4(4)? [closed]

This has been circulated recently. We all know the order of the calculation: BEDMAS. B rackets and Parentheses: First Priority E xponents: Second Priority D ivision: Third Priority M ultiplication: ...
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votes
1answer
205 views

Conveyor belt brain teaser [closed]

Okay folks, I'm keen to get a response to this brain teaser!!! Let's say you're looking at a conveyor belt... The width = 2m, and the length = 10m. Okay... This conveyor belt is moving from right ...
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1answer
377 views

Math sequence puzzle

Complete the sequence: 5928 1411 9909 1882 5419 ... It doesn't seem like a simple polynomial fit will work, I have tried the difference method and the quotient method. Any hint would be appreciated. ...
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5answers
282 views

You studied for this exam right?

Complete the exam, include your reasoning: 2 + 2 = 4 2 + 3 = 5 2 + 4 = 6 9 + 2 = 11 5 + 5 = 25 6 + 8 = 48 7 + 5 = __ 1 + 7 = __ 3 + 9 = __ (In the event someone wants to try to reason out my ...
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votes
2answers
427 views

When will the bacteria fill the test kit? [closed]

A test kit, is a gathering place for a colony of bacteria. This Colony, at 12 pm cell division has created a bacteria. Every minute, every bacteria is divided into two bacteria. 12: 43 (43 minutes ...
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3answers
481 views

The 3 Boxes Show! [duplicate]

A variation of the Monty Hall, where the values inside the choices are changed You were just out gambling and lost 5000 dollars! Of course being the gambler that you are, you pay 2500 to play this ...
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2answers
208 views

Find the correct sign

This is a question in a primary school book as a riddle. How can we put any mathematical sign (addition , subtraction, multiply and division) between five 5s to get the answer 66? 5 5 5 5 5=66
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3answers
230 views

Equality and Fraternity

Consider the "equation" $6145 - 1 = 6143$. Can you move two digits so as to create a valid equality? The equation $-127=-127$ is, of course, true. Suppose you were told again to move two digits as to ...
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5answers
230 views

Interesting card combinations [closed]

In a normal pack of playing cards (without jokers), the probabilities of the following events are the same: (1) Drawing a set of 4 different cards (irrespective of its color and suit) - let us call ...
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1answer
145 views

Winston the Hobo

Winston the Hobo really loves smoking. Every $7$ cigarette butts he finds on the ground, he rolls the tobacco in a cigarette and smokes it. Winston is very poor, so he actually rolls cigarettes with ...
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2answers
881 views

Combined numbers [closed]

Lets imagine we have two numbers (positive, whole numbers) $a$ and $b$ ($a>b$). We know that $a + b = 999$ and when we combine a and b, its scale is exactly $6$ for example: $a=888, b=111 $ $ \...