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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2
votes
1answer
115 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 ...
6
votes
2answers
675 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
98 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 ...
26
votes
5answers
4k 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
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7answers
2k views
-3
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1answer
145 views

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

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
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2answers
185 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
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0answers
72 views

Complete the series on this set of numbers [on hold]

Here is one that I can't seem to solve: Complete the following series: 529, 531, 542, 544, 561, 558
2
votes
2answers
206 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
4k 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
249 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
791 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
3k 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
726 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
11k 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
98 views

What should be the missing number? [closed]

What would be the missing number?
2
votes
1answer
268 views

What's the missing number?

$\begin{array}{ccc}6&7&4\\ 4&11&14\\ 13&2&11\\ 6&8&1\\ 15&3&?\end{array}$ Own attempt at building a puzzle, find 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
404 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
1k 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
116 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
149 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
108 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
46 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
40k views

Fill number in missing?

Given options are: A. 13 B. 42 C. 18 D. 30
-5
votes
4answers
151 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 ...
6
votes
4answers
381 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 ...
1
vote
1answer
82 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
310 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
124 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
393 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
468 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
170 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
592 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
97 views
6
votes
3answers
423 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<...
12
votes
5answers
741 views

Cup and Trade: The Perfect Nutmeg Soup

Your package from Orinoco has finally arrived! It's the Master Chef's Environmentally-Friendly Measuring Cup Set. It comes with 64 measuring cups having a volume of 1 cup, 1/2 cup, 1/3 cup, 1/4 cup, ....
56
votes
13answers
17k views

Are there eighteen or twenty bars in my castle?

Two friends, Mark and Rose, are very famous logicians; they are so clever that they can deduce any logic connection possible in a matter of minutes even from the most vague situation. Unfortunately, ...
1
vote
1answer
65 views

Figure out this Four digit Palindrome with two distinct digits and

The sum of the digits of the palindrome is Same as the number remaining after last two digits are removed.
9
votes
4answers
521 views

The Football Squad

The sixteen players of a football squad, wearing shirts numbered 1 to 16, have arrived in town for a tournament. At their hotel, they are assigned 16 rooms consecutively numbered. Moreover, each of ...
2
votes
1answer
112 views

Deduce Distinct Digits of the Given Fibonacci Sequence- Detail all Steps

$DEPUS$ $SRST$ $UDQD$ $CTQU$ $DTPR$ $PQR$ $SDE$ $VRR$ $CVV$ $DUU$ $QP$ $TT$
3
votes
1answer
158 views

Valiant Knight is back..but he is in grave danger from the Evil Queen

King has placed a bounty on Valiant Knight and enlisted his evil queen’s help. Queen knows knight’s regular stops of his journey and knows he goes through all odd prime cells. She strategically ...
21
votes
8answers
3k views

Robots in a spaceship

Xerxes has 6, 7 and 8-arm robots in his spaceship. Unfortunately, the 7-arm robots are misprogrammed and everything they say is a lie. The other robots are fine, they always speak the truth. Once ...
6
votes
1answer
404 views

Which Number Replaces the Question Mark?

Can you find out what the numbers below have in common? Can you figure out what comes next? ...
-3
votes
1answer
71 views

Strange? Primes and Palindromes have no business being in this Place?

$1$ $1$,$2$ Good easy start $1$,$2$,$4$ As expected $1$,$2$,$4$,$8$ I know it is going to be easy $1$,$2$,$4$,$8$,$16$ why is he giving this? I got it! $1$,$2$,$4$,$8$,$16$,Prime ...oops!.....
0
votes
1answer
74 views

How do you make Prime “COMPUTERS”?

$Given$: $COMPUTERS$ is the smallest Pan Digital containing all the digits 1 to 9 occurring only once. $COMPUTERSV$ is a Prime only when one of the correct digit ($V$)is added at the end. Also, $...
42
votes
17answers
8k views

A blanket for my baby snake

Mama snake wants to knit a blanket for little baby snake. She is not a dissipater and wants to make the blanket of a minimal size (area). But her baby snake is quite a lively baby and it always ...