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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.

0
votes
3answers
260 views

Rullo solving strategy for 2-4

How to eliminate/nominate candidates without guessing? For the 3s it's quite easy because of the odd numbers but how to get further?! For thoose who don't know the game, here's a short introduction:...
2
votes
1answer
161 views

Master and Slave versus Bob: easy version

Continuation of: "Sub-puzzle: Master and Slave versus Bob the Violent but Honest Psychopath" Continued in: "Master and Slave versus Bob: hard version" Previously I described a game that is played ...
10
votes
17answers
5k views

100 using only 5 number of digits

This is a problem from Martin Gardner. For each digit $1\leq d\leq 9$, make 100 using exactly five number of $i$s. Any operation is allowed, brackets as well. For $i=1,2$ I have a solution: $$100=...
2
votes
1answer
139 views

Row of alternating coin

I stumbled upon a mathematical puzzle that goes like this: You have 2n coins that alternate between head and tail. For example, if n=3, then it looks like H T H T H T, where H = head and T = tail. To ...
8
votes
2answers
212 views

A CrossNumber puzzle with a twist

Here's an interesting puzzle which I discovered the solution to yesterday. The eleven grid entries in increasing order are $A, B, C, D, E, F, G, H, I, J, K$, and you are given the following hints. ...
1
vote
1answer
226 views

What is the value of X?

24 6 63 132 4 14 23 x 17 The answer is either : 21, 14, 3 or 2
1
vote
1answer
216 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 ...
1
vote
3answers
280 views

Sub-puzzle: Master and Slave versus Bob the Violent but Honest Psychopath

[I created this as a sub-puzzle to "Strategy to beat the Casino reversed", that has been sitting unsolved for months. You may wish to read that puzzle first, but this is self-contained. My answer to ...
4
votes
1answer
144 views

More Email Shenanigans

I don't know how these people know my email address, but after the (still unsolved) shenanigans of the Interesting email I received? I got... yet another email. This one was of a Google Drive document ...
4
votes
0answers
256 views

My brain froze trying to solve this [closed]

Try to figure out the missing numbers!
5
votes
2answers
168 views

Using 20, 17, 16, 8, 7 to make 9

You can use $+, -, \times, $ or $/$ (namely $\div$). Use all five numbers (20, 17, 16, 8, and 7) only once to make $9$. From what I've been told there are $4$ answers. The only one I've been able ...
2
votes
1answer
128 views

Some Really Confusing Math

I was talking to a co-worker this morning and he stated that he was able to make both of these statements true using only $1, 3, 5,$ or $ 7$. He then proceeded to tell me: $1 = 5$ $2 = 4 + 7$ $3 = 1$ ...
3
votes
2answers
429 views

Which polygon is the one?

There is a unit-radius circle and you must form a polygon all of whose vertices are located on the circle, such as below: What is the biggest possible value of the sum of squares of side lengths of ...
5
votes
2answers
1k views

Did Grandpa count correctly? Another Grandpa Mystery

Grandpa just returned from a long trip. He started telling me about his adventure in a wild place. " I saw animals", he said. "Three different kind" "Just for fun I counted their limbs" "...
21
votes
9answers
5k views

Google's 20th Anniversary: Make 20 using 6 0 0 6 1 3

Belated 20th Happy Birthday to Google (600613)! Challenge: Use 6, 0, 0, 6, 1, 3 to make the number 20. Rules: Use all numbers, in that exact order. Allowed operations: +, -, x, /, sqrt, (); no ...
7
votes
6answers
3k views

Use 6, 5 and 3 to make 57

Assemble a formula using the numbers $5$, $6$, and $3$ in any order to make $57$. You may use the operations $x + y$, $x - y$, $x \times y$, $x \div y$, $x!$, $\sqrt{x}$, $\sqrt[\leftroot{-2}\uproot{2}...
13
votes
9answers
2k views

Use 0, 5, 7 and 1 to make 89

Assemble a formula using the numbers $5$, $0$, $1$, and $7$ in any order to make 89. You may use the operations $x + y$, $x - y$, $x \times y$, $x \div y$, $x!$, $\sqrt{x}$, $\sqrt[\leftroot{-2}\...
1
vote
2answers
103 views

Is this possible ( - ) + + - - - = 100 I can do many other way

Insert the numbers 1-9 inclusive each only once into the calculation to arrive at the answer 100. ( - ) + + - - - = 100 Is this possible?
0
votes
2answers
178 views

Can you solve the riddle

Can you solve the mathematics puzzle?
1
vote
4answers
102 views

Air Miles Challenge

This isn't my own creation, it's an exercise that my partner had to do during a work exercise and seemed interesting to share here. You've been given 86,400 Air Miles to explore the world and there'...
14
votes
2answers
423 views

Cross-number puzzle

ACROSS: A. a square C. a multiple of N Across E. (C Down) $\times$ (I Across) G. a square root of A Down I. a square root of D Down J. (J Across) $\times$ (K Across) = (F Down) $\times$ (M Down) ...
6
votes
2answers
159 views

A Crucial Delivery

Planet Earth has been at war with the nefarious aliens of Planet XYZ for a while. The front lines are on Planet XYZ, and you, being Earth's lead scientists, need to find a way to get vital information ...
-2
votes
3answers
133 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 ...
5
votes
4answers
176 views

The athletes puzzle [closed]

Athletes arrange themselves into $x$ rows and $y$ columns. We pick the tallest of every column and name the shortest of them A. We pick the shortest of each row and name the tallest of them B. ...
12
votes
5answers
4k views

Hard 4x6 chocolate bar Riddle

You have the following 4x6 chocolate bar. The question is what is the least amount of cuts you have to do in order to create 24 pieces of 1x1 chocolates. the cuts can have any shape they want as long ...
8
votes
4answers
310 views

A “Find the Path” Puzzle

I invented a puzzle, inspired by Simon Tatham's Portable Puzzle Collection. Is there anything that it could improve on? Was it too easy, or was it too hard? Anything I could add? What must I call it? ...
3
votes
2answers
161 views

Third and Triple

This is inspired from Half and Double Value. Please see that puzzle, too. Okay, so now you're really bored. A good puzzle wastes time, so you make one. Try to find the smallest number, that, when ...
16
votes
2answers
323 views

If you have 3 random numbers between 1 and 27 can guess the fourth?

Problem: Ashley and Ivan want to impress their friends and come up with a magic trick: One of their classmates comes up with 4 unique random numbers between 1 and 27 and tells them to Ivan. Ivan ...
3
votes
2answers
142 views

$109088$ as sum of $3$ palindromes

One can write the number $109088$ as the sum of two palindromic numbers as follows: $$109088 = 99199 + 9889$$ Note that the numbers on the right are both palindromes (read the same left to right as ...
-4
votes
1answer
88 views

Will these two kangaroos meet ever? [closed]

We have two Kangaroos. First one starts from point S1 and jumps for distance D1 in one jump. Second one starts from point S2 and jumps for distance D2 in one jump. Both will jump along the number line,...
9
votes
0answers
180 views

A small team doing their job

Find the unique solution to $$ 5\,ninja + retook + quarter + turn = \_\,\_\,\_\,\_ + \_\,\_\,\_\,\_\,\_\,\_\,\_\,\_\,\_\,\_ $$ where each unknown is a different _ _ _&#...
4
votes
1answer
146 views

Palindromic number puzzle - make 505 from 20202

Can you assemble a formula using the numbers $2$, $0$, $2$, $0$, and $2$ in any order so that the results equals $505$. You may use the operations $x + y$, $x - y$, $x \times y$, $x \div y$, $x!$, $\...
4
votes
3answers
1k views

1984 - take the digits 1,9, 8 and 4 and make 123 - Part III

Part III ... Next year is the 70th anniversary of the publication of the book 1984 by George Orwell. Here is a puzzle to start the anniversary celebrations off a bit early ... I think this is the ...
6
votes
3answers
385 views

Calculator Bomb

So, I need your help. I got home after a long day and found a calculator roughly taped to my door. However, there was something much more disturbing attached to that calculator. It was some kind of ...
7
votes
4answers
171 views

Fill in the boxes to get the right equation v2

My take on a recent puzzle. Place numbers into boxes to create a correct equation, using each number at least once: $$\Box-\Box+\Box\times\Box=\Box\:/\:\Box$$ This time the four decimal numbers are ...
1
vote
2answers
100 views

A Fairly Simple Equation #2

I got a lot of positive feedback on my last puzzle, A Fairly Simple Equation (even though it was apparently a lot easier than I thought it would be!) So, I've got another similar puzzle. General ...
3
votes
3answers
150 views

A Simple Math Puzzle

So my last math puzzle was too easy apparently, and this one might be too. Either way, the rules are the same. No rotation. No duplication. No combination. No rounding. No computers. Good luck to ...
6
votes
3answers
530 views

My First Math Riddle

Okay, so I write a lot of Riley and story riddles; however, I've noticed that I like the mathematical riddles too! I decided to write one, and I hope you all enjoy it. A few rules: No rotation. No ...
8
votes
3answers
423 views

A Fairly Simple Equation

I'm new, so I thought I'd start with a fairly simple puzzle.(Simple doesn't necessarily mean easy.) Can you fit the numbers $2, 3, 4, 5, 6,$ and $10$ into this equation, each replacing one letter, so ...
10
votes
7answers
771 views

Fill in the boxes to get the right equation

Here is a math puzzle I had a little bit of hard time with No computers please There is a solution without inverting 6 to 9
1
vote
4answers
244 views

Use the digits 1, 9, 9, 8 to get 81 [closed]

Using the digits $1, 9, 9$ and $8$ in that order, and the operations $+$, $-$ and/or $\times$ in any order between pairs of digits, create an expression that equals $81$.  Normal precedence rules ...
3
votes
4answers
1k views

1984 - take the digits 1,9, 8 and 4 and Hard Challenges!

This is kinda follow up question to: Part II... Next year is the 70th anniversary of the publication of the book 1984 by George Orwell. Here is a puzzle to start the anniversary celebrations ...
1
vote
3answers
166 views

1984 - take the digits 1,9, 8 and 4 and make 369

Part II... Next year is the 70th anniversary of the publication of the book 1984 by George Orwell. Here is a puzzle to start the anniversary celebrations off a bit early ... Warm up Can you ...
1
vote
1answer
140 views

1984 - take the digits 1,9, 8 and 4 and make 246

Next year is the 70th anniversary of the publication of the book 1984 by George Orwell. Here is a puzzle to start the anniversary celebrations off a bit early ... Warm up Can you assemble a formula ...
14
votes
11answers
17k views

Find out the correct number

Find out the correct number to replace the question mark. Source: Beijing Aidi International School summer test (2018-08-21). Author: 坦途国际教育
4
votes
1answer
115 views

A Math Puzzle with a Pattern

Inspired from a puzzle marathon, here is a math puzzle. There is a pattern with this set of numbers (not in the creation though). According to the pattern, what is the logical replacement for the ...
0
votes
4answers
350 views

Use 2, 0, 1, and 9 to make 34

Use 2 0 1 and 8 to make 67 See above for the rules. Note that in this one, the year is $2019$, not 2018 Whoever does this one will be rewarded with the answers for 1-100. Hint
7
votes
1answer
843 views

Use 2, 0, 1 and 8 to make 199

Assemble a formula using the numbers $2$, $0$, $1$, and $8$ in any order so that the result equals $199$. You may use the operations $x + y$, $x - y$, $x \times y$, $x \div y$, $x!$, $\sqrt{x}$, $\...
-5
votes
1answer
68 views

What is the pattern that describes these numbers? [closed]

Supposed you are given the following numbers: 6 28 496 8128 33550336 8589869056 What's the relation between them?
10
votes
7answers
2k views

Matchstick Puzzles

Puzzle #1: There is a matchstick: | Add 2 more matchsticks to make the number, 11. Puzzle #2: There is a palace made out of 11 matchsticks: Move 2 matchsticks to make 11 squares. Puzzle #3: ...