# 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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### Lockpicking combinations [on hold]

A locksmith uses the tool below to pick a tumbler lock with 6 pins and 6 possible pin heights. Suppose she already knows the correct sequence in which to try the pins. How many combinations will she ...
642 views

### Ernie and the Superconducting Boxes

I was in anticipation all last week. Ernie, who had been travelling for several months, was finally coming home. So over the weekend I dropped in on him. He was bursting with news. "Some wonderful ...
277 views

### What is a NaturaW Word™?

This is in the spirit of the What is a Word/Phrase™ series started by JLee with a special brand of Phrase™ and Word™ puzzles. If a word conforms to a special rule, I call it a NaturaW Word™. Use the ...
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### A Magic Diamond

Place 15 different positive integers on the vertices of this graph so that the ten products of three numbers in a straight line are all equal.
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### Big number puzzle

I saw this on rec.puzzles many years ago, but can't find the reference to credit the source. I am thinking of a large number. If you want to multiply it by a two digit number $ab$ with $a \lt b$, ...
147 views

### Hunting for treasure in 1-d grid [duplicate]

In a castle, there are N rooms in a line. Each room has a door to the two neighbouring rooms (or the one neighbouring room, for the rooms at either end). A treasure is hidden in one of the rooms. ...
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### Missing Piece of Pie - Can you find it?

A piece is missing! What should it be?
180 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 ...
233 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. ...
81 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
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### 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 ...
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 ...
273 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 (...
828 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 ...
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 ...
737 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, ... ...
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### 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), ...
114 views

### What should be the missing number? [closed]

What would be the missing number?
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 ...
409 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: ...
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### 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)) ...
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### 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 ...
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### 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 ...
127 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 ...
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