## coin play

Posted on: January 29th, 2014 by
1

A large bag of coins is emptied on the floor such that no two coins overlap each other.
1. A child randomly selects a coin on the floor.
2. If the coin is heads, the child turns it over to show tails.
3. If the coin is tails, the child flips the coin in the air and likr before, doesn't overlap another.
4. He then goes to #1
After this process runs for a long time, comment of the the proportion of heads and tails in the room.

- via Quora

## The image tells the answer

Posted on: January 28th, 2014 by
1

Look at the image below and write the answer.

## Hat puzzle

Posted on: January 27th, 2014 by

5 girls stand in a circle. Each girl wears a red hat or a blue hat. Each girl is blind-folded and is told the hat color of the two people adjacent to her on the circle. The five girls need to come up with a strategy to guess their hat colors simultaneously. Is it possible?

## Average speed

Posted on: January 26th, 2014 by
5

Suppose a bicycle's average speed in any 10 minute interval is 18 miles per hour. How much distance will the bicycle travel in 25 minutes?

## Number operations

Posted on: January 25th, 2014 by
1

Suppose you are playing with fractions 1,1/2,1/3,.... 1/100. At each step, you take two of the fractions x,y and replace them by a function f(x,y). You keep repeating this process until only one number remains. What are all the possible values that the remaining number can take if f(a,b)=ab+a+b? Can you solve the puzzle again if f(a,b)=ab/(a+b)?

## meta puzzle

Posted on: January 24th, 2014 by

What does this mean? "meta meta meta meta".

- via Gpuzzles

## Solve

Posted on: January 23rd, 2014 by
1

Solve for integers x, y: $19x^3-84y^2=1984$.

- via Russian Math Olympiad practice problems

## Cut a square

Posted on: January 22nd, 2014 by

Can you cut a square into 8 acute angled triangles?

- via Russian Math Olympiad practice problems

## Hitori

Posted on: January 21st, 2014 by

Try a game of Hitori.

The object of Hitori is to eliminate cells in the grid until there are no duplicates in any row or column. To eliminate a cell, it must be turned black by clicking on it. You must do this, however, without placing any black cells next to each other on a side (touching diagonally is ok) or by placing black cells in such a way that any white cells on the board are cut off from the rest of the white cells. You can also mark cells in this game as circled by clicking a second time or right clicking. This is just for your own visual reference as these cells count as white cells. This can be useful as the game progresses to visually mark the cells you know cannot be black. When you think you have solved the puzzle, click 'Check'..Good Luck! If you would like some hints on how to get started, be sure to check out the 'Strategy Hints' link below.

## Racing in an escalator

Posted on: January 20th, 2014 by