66 arithmetic questions.

17 A partition of 1000 into nine parts

1 answers, 451 views number-theory graph-theory arithmetic
The sum of nine whole numbers is 1000. If those numbers are placed on the vertices of this graph, two of them will be joined by an edge if and only if they have a common divisor greater than 1 (i.e. ...

13 My Three Children

The sum of the ages of my three children is 40. Though the ages of my two daughters are relatively prime (i. e. they have no common divisor), the age of each of them does have a common divisor greater ...

20 A Tour Around a Triangle

1 answers, 666 views number-theory graph-theory arithmetic
Place the 18 even integers between 2 and 36 in the empty nodes of this triangular graph in such a way that if a path is drawn by coloring in red all the edges joining any two nodes whose numbers add ...

5 Six sisters on the ski lift

1 answers, 309 views number-theory arithmetic
The sum of the ages of six sisters known to me is 92. Though there is no single whole number greater than 1 that simultaneously divides the ages of any three of them, I did notice this morning, while ...

20 The 10,958 Problem

Here is the task: Write down 10958 using all 1-9 digits in ascending order and only one time. You are allowed to: 1) group digits into numbers 2) use 5 basic operations: + - * / ^ ("^" ...

10 Four Marathon Runners

3 answers, 1.143 views number-theory arithmetic
Four marathon runners, each identified with a positive whole number, sit around a table. Each of them notices that their own number has a common divisor with the number of the runner sitting on his ...

1 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), ...

-3 Calculate cost of excess water consumed [closed]

1 answers, 104 views calculation-puzzle arithmetic
100 Liters of water is available equally in a month for consumption among 5 members @ 1 dollar per liter. If some members don't use their own available 20 liters, it can be used by the others at the ...

15 A partition of 100 into nine parts

3 answers, 1.909 views mathematics graph-theory arithmetic
The sum of $9$ positive natural numbers, not necessarily distinct, is $100$. If placed appropriately on the vertices of the following graph, two of them will be joined by an edge if and only if they ...

5 The mathematical quiz

5 answers, 388 views mathematics arithmetic
There are 4 equations. What should I put in place of the ? in the last one?1 + 4 = 5 5 + 3 = 11 7 * 7 = 61 10 - 1 = ?

3 Curiosity of February 5$^{th}$

5 answers, 575 views mathematics arithmetic time
Some people write February 5$^{th}$ using the md format, as $2.5$ or alternatively as $2/5$. Note that $2.5 \times \frac25 = 1$. Is there any other date satisfying $a.b \times \frac{a}{b} = 1$? ...

8 My forgotten PIN

3 answers, 473 views number-theory arithmetic
I´ve forgotten my PIN, a four-digit number. All I remember is that it is a perfect square, and that it has at least one digit in common with every other four-digit square number. What is it?

13 My five daughters

5 answers, 4.240 views number-theory arithmetic
The sum of the ages of my five daughters is 43. The ages of any two of them have a common factor greater than 1. How old are my daughters?

8 A unique partition of 200 into 6 parts

2 answers, 713 views number-theory arithmetic
The sum of six positive integers is 200. If placed appropriately on the vertices of this graph, two of them will be joined by an edge if, and only if, they are not relatively prime, that is, if they ...

7 Videogame salesmen

Two gamers sell their collection of XBOX games. They've got as many Euros as there were games in the collection originally for each game. They split the money by having the first gamer take 10 Euros ...

Continue sequence

2 answers, 186 views number-sequence arithmetic sequence
Son asked such a task. Continue the number sequence5, 7, 8, 12, 11....The son is in the second grade. They studied the operations of addition, subtraction and ...

6 How many multiplications to find n^k given n, for general k?

1 answers, 452 views mathematics optimization arithmetic
I was looking at the nice puzzle Find $n^{23}$ with the least multiplication. My first instinct for this would have been to find $n^{2^i}$ for each $i$ first and then multiply these together as ...

-6 What's My Number (Math Riddle) [closed]

1 answers, 448 views mathematics arithmetic
I am thinking of a number. I multiplied by 3, subtracted by 8, doubled the result, and added 14. Then i added on 50% of what I had and subtracted 11. Then i divided by 5. After all that, I was left ...

-4 Series Problem By Gpuzzles - I Have Doubt [duplicate]

1 answers, 289 views mathematics arithmetic
gpuzzles.com is one of my favorite sites along with StackExchange, but can someone please elaborate on the answer? Problem: Can you solve the number series problem by replacing boxes with numbers 1, ...

9 Sum self enumerated digits

Please fill in the entire summations for lines 4 through 9 and just the total for line 1,000,000.         1.     1   =   1   ...

14 Why you shouldn't buy cheap puzzle books

Backstory contains important information, but nothing hidden. Also, tl;dr parts are bolded, but I can't guarantee I didn't forget bolding some part. Recently there's been a grid-deduction craze here ...

2 Turn based Number game

1 answers, 156 views strategy game arithmetic game-theory
You and a friend take turns saying positive integers greater than one. You can't say a number that is a multiple of previous numbers or a sum of multiples of previous numbers. For example, if A says 3 ...

5 How old was Matthew when his brother died?

When Sam's father died, Sam's uncle, Matthew (his fathers only brother) was twice the age of Sam minus 14 years. As Sam and Matthew grew older they became friends. When the younger of the two turned ...

2 Complete the equality (medium-hard)

Complete the equality to make it true:1 1 1 1 1 = 945Using similar logic, solve for this:1 1 1 1 1 = 80Info: You should ...

4 Complete the equality

4 answers, 262 views mathematics arithmetic
Complete the equality to make it true:1 1 1 1 = 5You can add any math operation or symbol to the left side. You cannot change right side nor the ...

4 Remove two digit/symbol to find equality

1 answers, 134 views mathematics arithmetic
Find the equality by removing any two digits or symbols (of course, except equal sign) $4\div3+63=9-23\times7\div3$ For example, if the equation below was given, Example: $91-81=45+12\div3-85$ ...

15 Buttons on an old non-scientific calculator are less sensitive

All 5 numbers are entered in an ascending order. These numbers are in an arithmetic progression. The value of the fifth number, i.e. the largest number, is less than 99. While adding these ...

13 Yet another matchstick puzzle

14 answers, 3.078 views arithmetic matches
Inspired by this post, here there is my attempt at a matches' puzzle. The expression 1 = 850 - 9 - 6 is obviously wrong: move exactly three matches to obtain a correct expression. Rules are: This ...

6 Difficult sequence

Here I go : $3 + 5 + 6 = 15 \ 18 \ 72$ $5+ 5 + 6 = 25 \ 30 \ 94$ $5 + 6 + 7 = 30 \ 35 \ 85$ $5 + 5 + 3 = 25 \ 15 \ 73$ $9 + 4 + 7 = 36 \ 63 \ ?$ Replace ? with appropriate number

8 Little Red Solving Hood goes one-stop swapping

1 answers, 336 views arithmetic computer-science
Moral of the story:   Two stored values may be swapped arithmetically with 4 or fewer variable references. Puzzle of the story:   Can you exemplify the moral?   (With 10 or ...

Two Three-Digit Numbers Added to Make Four-Digit Sum. No Number Can Repeat Itself.

A friend posed this question to me a few days ago, and I just haven't been able to get it off of my mind. "There are ten numbers from 0 to 9. You can use any number you like in the box, but the ...

10 The Vacuumed Quotes

1 answers, 543 views cipher arithmetic
A colleague of mine likes to put his favorite quotes up on the fridge using those little magnetic letters. This morning the cleaner came and accidentally vacuumed up all the letters. We were able to ...

12 KenKen Zen: A journey begins

Let us shy away from the materialistic opulence of 361- cell KenKen layouts (−9 to +9, squared).  Let us contemplate a modest KenKen journey, unburdened by gratuitously ...

4 The Autonumerigram Challenge [duplicate]

Some phrases both refer to a number, n, and are comprised of n alphabetic characters. I call any such phrase an autonumerigram. For example, four has 4 letters seven plus seven has 14 letters ...

3 KenKen Zen: The Cluelessening

As our KenKen voyage of cluelessening­* began, some clues remained entirely hidden from us.  Though much remains to be discovered, we may now be entrusted with all clue amounts at once.&...

Fill 3x3 magic square with distinct numbers 1..60 summing up to 69

I have to fill a whole 3x3 grid in such a way that the sum of each row, column, and main diagonal is 69. I couldn't find any logic to fill it up. I have to use distinct numbers from 1 to 60 for this. ...

31 Sum other numbers

4 answers, 1.607 views lateral-thinking arithmetic
Begin with a flagrantly erroneous summation and a woefully vacant substitution table. 234 + 5 Digit 2 3 4 5 6 7 8 ------- ...

19 Honeydripping around the clock

What path could a honeybee follow, beginning and ending at top center, visiting every empty cell exactly once and dripping 2 drops of honey into the last cell? Start ...

9 H-one-one-oneycomb

What path could a honeybee follow to fill all cells with honey, beginning and ending at the center and visiting every cell exactly once? At first the only ...

10 How to fill a honeymoon

How can a honeybee visit all cells exactly once in this crescent shaped honeycomb, beginning at the bottom tip and ending at the top? The starting cell, at ...

3 Get the largest number using the crazy circuit board

There is a crazy circuit board with three kinds of elements which can change the signal value. All intersecting paths are connected (but paths touching by a single point are disconnected). There is ...

3 Arithmetic Puzzle

1 answers, 154 views puzzle-identification arithmetic
The British Independent and i newspapers run what they call an "Arithmetic Puzzle", which comprises a grid of nine cells, with each cell separated from the others by arithmetic symbols: (+ - / *), and ...

1 It is related to a type of mathematics game

2 answers, 224 views formation-of-numbers arithmetic
Start with two digits from $1\dots9$ to form a $2$-digit number. Multiply this number by a single digit from $1\dots9$. Add the result to another two digit number from $1\dots9$, and calculate the ...

-6 A (Simple) Arithmetic puzzle

3 answers, 396 views mathematics arithmetic
I'm hoping this one was not posted here already, tried to search a bit and didn't find it. It's a really nice brain teaser: Add arithmetic operators (plus, minus, times, divide) to make the ...

32 A moderate visual number puzzle

2 answers, 1.514 views visual arithmetic
In the following diagram, each red dot represents a positive number. The dot-numbers on each of the five circles spell out either a word (each dot corresponding to a letter) or a number (each dot ...

5 Age of Samantha and her grandchildren

Samantha is suffering from Alzheimer's and uses math to help remember things. Samantha has two grandchildren. Samantha youngest grandchild's age when raised to the power of the square root of her ...

-3 In which year(s) could I have been born, if you know my unexact age in an unexactly dated source (unexact means exact up untill years) [closed]

1 answers, 181 views calculation-puzzle arithmetic
At some point in 2015 I filled out a form and wrote 41 for my age. What are my possible birth years? Some trivial clarification about the information above: The age 41 is only exact up until the ...

9 The oldest wins the prize, but they won't tell their age

I'm trying to design a problem that should be as close as possible to the following setup, while meeting some requirements about its solutions. Initial setup There is a group of more than 2 people ...

5 Find age of John

2 answers, 403 views mathematics arithmetic
Ten years before Alice's age is 4 times John's age. Ten years later, Alice's age is 2 times John's age. How old is John?

53 XOR - Is it possible to get a, b, c from a⊕b, b⊕c, a⊕c?

Just got a simple question from a friend; still thinking. Let's share it! Is it possible to get a, b, c when you have a⊕b, b⊕c, a⊕c ?where ⊕ is the boolean ...