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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.

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3
votes
1answer
217 views

Missing Number in a Seven Segment Circle

What number should replace the question mark? Please be helpful. If you have the answer, please reply to this post with the explanation and answer. If you don't have the answer, then don't comment. ...
2
votes
1answer
330 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 ...
7
votes
2answers
306 views

Alice and Bob play at cards

To pass the time Alice and Bob play a simple game of chance where cards are drawn in pairs from a shuffled standard 52-card deck. If two red cards are drawn Alice wins the round. If two black cards ...
0
votes
1answer
108 views

What value will be replaced by question mark? [closed]

I can't find any answer The options are: (a)18. (B) 16. (C)10. (D)12!
3
votes
0answers
202 views

Find the missing element?

I've been trying to solve this for quite some time, can you help me solve it? This puzzle was made by one of my friend's teachers. This is not copyrighted and cannot be found anywhere on the internet. ...
-2
votes
2answers
181 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)
11
votes
2answers
3k views

The grades of the students in a class

You are a new Math 102 professor in a university class of 88 students and would like to learn their grades from previous semester to know your students better and put a note of it to get an idea how ...
-9
votes
1answer
143 views

What number I am? [closed]

I am a 4 digit number The digit in the ones place is 6 The value of the digit in the hundreds places is 500 The digits in the tens and thousands places are the same and they add up to 8 What number I ...
12
votes
6answers
724 views

Use 0 1 2 3 4 to form 9 3-digit numbers

Use $0, 1, 2, 3, 4$ to make the any of these numbers: $$331, 333, 435, 452, 455, 458, 461, 469, 470$$ You must use all $5$ digits $0, 1, 2, 3, 4$ each exactly once. You can make multi-digit ...
10
votes
2answers
433 views

#, %O, and so on

I woke up this morning to find someone had added a new button to my basic calculator. Besides the $+$, $-$, $\times$ and $\div$ buttons, there's now also a $\#$ button. I figured, "Well, this probably ...
2
votes
1answer
226 views

How to solve the input output puzzle?

Here's the puzzle I am solving daily input-output challenge questions in the gradeup android app in order to take preparation for SBI (State Bank of India) PO (Probationary officer). Here I came ...
18
votes
3answers
5k 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
1answer
357 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
1answer
195 views

Four coins on my desk

I have four coins, all of which are United States currency, on my desk. Some of these coins are face up, and the rest are face down. I know the following facts about the four coins: 1) Each of the ...
5
votes
2answers
701 views

Legal advise for a family dilemma

"A client of mine," said a lawyer, "was on the point of death when his wife was about to present him with a child. I drew up his will, in which he settled two-thirds of his estate upon his son (if it ...
4
votes
1answer
120 views

The ultimate conversion of a square into right angle pyramid

This is a follow up of other puzzles. Here a general case of which the other cases are a subset. Given a square of any size, cut it into four pieces to be reassembled into a right angle pyramid (the ...
27
votes
5answers
5k views

An unusual and very hard number sequence problem

I heard this number sequence problem about 25 years ago from a maths lecturer. What number should go in the place of the question mark in this mathematical sequence: $..., 30, ?, 60, 90, 140, 225, ...
11
votes
7answers
2k views

Missing Piece of Pie - Can you find it?

A piece is missing! What should it be?
-3
votes
1answer
675 views

we are five we have three thousand four hundred fifty who are we? [closed]

we are five we three thousand four hundred fifty, who are we ?. Its a riddle like question but stranded with getting the answer for this question , am very sure the answer will make me slap my head ...
3
votes
2answers
256 views

5 Precommitting Pirates Puzzle

Another variant of the Pirate Puzzle, inspired by this variant and a bit more complex. Scenario: Five pirates of different ages obtain 100 gold pieces in total, and want to decide how to split them. ...
2
votes
0answers
83 views

Complete the series on this set of numbers [closed]

Here is one that I can't seem to solve: Complete the following series: 529, 531, 542, 544, 561, 558
1
vote
2answers
259 views

Minimize sum of guesses to win lottery

Ten boxes are given with $a_1,a_2,a_3,a_4,a_5 ......a_{10}$ number of balls in them respectively .These boxes are randomly ordered but $a_1,a_2 .....a_{10}$ is told.We can arbitrary select a box and ...
8
votes
3answers
5k views

How to make 21?

How do you make $21$ from the numbers $1$, $5$, $6$, and $7$? You can use the operations of addition, subtraction, multiplication and division, as well as brackets. You must use each number exactly ...
5
votes
1answer
295 views

5 Negotiating Pirates Puzzle

5 pirates of different ages have a treasure of 100 gold coins. On their ship, they decide to split the coins using this scheme: The oldest pirate proposes how to share the coins, and ALL pirates (...
8
votes
2answers
912 views

5 Pirate Puzzle Question

Question: 5 pirates of different ages have a treasure of 100 gold coins. On their ship, they decide to split the coins using this scheme: The oldest pirate proposes how to share the coins, and ALL ...
23
votes
8answers
4k views

How to choose at least half of everything

Some number of gold, silver, and copper coins are scattered in $N$ chests. You may look into each chest and count each type of coin in them, and then select $M$ of the chests. Your goal is to have at ...
8
votes
2answers
749 views

IX-NAY on the IX-SAY

Will this sequence ever have a 6 in it? 9, 1, 1, 1, 10, 3, 1, 1, 10, 5, 1, 1, 10, 1, 5, 2, 1, 1, 10, 1, 1, 1, 5, 4, 1, 1, 10, 3, 1, 1, 5, 1, 1, 1, 5, 2, 1, 1, 10, 5, 1, 1, 5, 3, 1, 1, 5, 4, 1, ... ...
2
votes
10answers
15k views

Make numbers 1-30 using 2, 0, 1, 9

This is very similar to the 2, 0, 1, 8 problem. Just try to make all numbers 1-30 using the digits 2, 0, 1, 9. Rules: Use all four digits exactly once Allowed operations: +, -, x, ÷, ! (factorial), ...
2
votes
0answers
120 views

What should be the missing number? [closed]

What would be the missing number?
16
votes
9answers
7k views

Salesman's claim for mechanical keypad lock - 5 buttons and 545 combinations!

A company makes mechanical keypad locks. The keypad is a set of five buttons arranged vertically. O O O O O The buttons are quite close together. Once a ...
3
votes
2answers
410 views

Grandpa's Numbers

Grandpa likes pencils but not pens Grandpa likes Beijing but not Tokyo Grandpa likes math but not chemistry Grandpa likes Contact but not _______ Make sure to explain! Hint 1: Hint 2: ...
11
votes
6answers
2k views

Some interesting calculation puzzle that I made

So I'm creating some kind math puzzle that goes like this: 1=-2+3 12=3*4 123=(4*5)+(6+7)*8-9+10 (thanks JS1 for finding shorter one) 1234=(5*6*7*8)-(9+10+11+12+13+14+15+16+(17*18)+19+20+(-21+22)) ...
31
votes
8answers
10k views

How many cars does the millionaire have?

I had a logical riddle on a programming interview test which was something like this: In his garage a millionaire had cars, of which only 2 were not white, only 2 were not green and only 2 were not ...
16
votes
3answers
1k views

The maximum number of SETs with six cards

The SET game works with a deck of $81$ cards. Each card contains a set of symbols with four attributes: color (red, green, purple), shading (empty, striped, or solid), shape (oval, squiggle, or ...
2
votes
1answer
135 views

Oops! Mixed up Multiplication - Needs to be Fixed

$Given$: $U$, $V$, $C$ are distinct digits, varying from 1 to 9. $U$ > $V$ > $C$ $UVC$, $VCU$, $CUV$ are concatenated Numbers $(UVC)*(VCU)*(CUV)$ = $234235286$ The digits on the right hand side ...
24
votes
4answers
2k views

Savage Road Signs

There is a highway that starts in the city of Savage. You must must place distance marker signs on this highway for the outgoing traffic. According to highway code, there must be a distance marker ...
1
vote
2answers
162 views

Is it possible to reach 00?

Ann and Bob are going to play a game. Ann chooses a two digit numbers from 01-99. Bob then mirrows the number and adds the checksum to this number and announces the result to Ann. The players then ...
2
votes
1answer
118 views

What is the Last Digit in the Result of the given Expression? [closed]

$Given$: $ASC$ is a concatenated number with distinct digits. $S$ is square of $A$, $C$ is cube of $A$ Deduce the last digit of the following Expression through Deductive Reasoning only: $$\begin{...
1
vote
1answer
54 views

Pan Digital Split among Two Powers

$Given$: $AB$, $DBCE$,$AGFPQR$ are three concatenated numbers with all distinct digits varying from zero to nine. $AB^C$ = $DBCE$ $AB^F$ = $AGFPQR$ Deduce all the digits through logical reasoning ...
3
votes
6answers
45k views

Fill number in missing?

Given options are: A. 13 B. 42 C. 18 D. 30
-4
votes
4answers
163 views

Go for the Gold

You are given a bag containing 1 and 2 ounce gold rounds. You need to draw one coin at a time till they Sum up to ten rounds. How many different ways you can achieve that? What is the quickest path ...
1
vote
1answer
91 views

Express the given Fractions as Continued Fractions

Using only the numbers, $1$, $2$, $12$. No concatenations allowed. Only permitted signs are plus and division. Brackets are not needed. Expressions should be as concise as possible. Typical ...
1
vote
2answers
319 views

I need help to solve this puzzle

This puzzle was shared by a friend, who in turn got it from school, and there is no competition involved. We have been working on it for a long time without any answers at all. Can anyone help me find ...
4
votes
3answers
138 views

Make 2019 Factorial Multiplication a perfect square

N is not a square number and consists of 2019 factorial multiplication as shown below: $N=1!\times 2!\times 3!\cdots 2018!\times2019!$ At least how many factorial needed to be removed from the ...
4
votes
1answer
398 views

Find my two numbers

Find my two numbers: Both are positive integers. Their difference is a prime. Their product is a perfect square. Their sum's last digit is 3. Bonus: Can you show how many solutions exist?
8
votes
1answer
474 views

Relevant primes

Let's call a prime number $p$ "relevant" if there exists an integer $n>1$ such that the integer part of the sum $$ \sum_{k=1}^{p^n} \sqrt[n]{\frac{1}{k^{n-1}}}$$ is $2016$. How many "relevant" ...
3
votes
1answer
192 views

Holy Alphabet Arithmetic

$Given$: $A$+$B$+$C$=3 $B$+$C$+$D$=3 $C$+$D$+$E$=1 $D$+$E$+$F$=1 What is $E$+$F$+$G$=?
12
votes
2answers
609 views

The Puzzling Reverse and Add Sequence

The sequence of numbers 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 11, 22,... (A056964 in the OEIS), in which the nth term equals n+reversal of digits of n, poses a number of intriguing puzzles. Here just ...
-5
votes
1answer
110 views
6
votes
3answers
428 views

Guessing a number with 250 divisors

Alice and Bob play the following number guessing game. First Alice picks an integer $n$ with exactly $250$ positive divisors. These divisors include $1$ and $n$, and are denoted as $1=d_1<d_2<...