You have two jars, 50 red marbles and 50 blue marbles. You need to place all the marbles into the jars such that when you blindly pick one marble out of one jar, you maximize the chances that it will be red. When picking, you'll first randomly pick a … [Continue reading]

## Ants on a triangle

There are three ants on a triangle, one at each corner. At a given moment in time, they all set off for a different corner at random. What is the probability that they don't collide ? … [Continue reading]

## Balls in a bag

You have 20 blue balls and 14 red balls in a bag. You put your hand in and remove 2 at a time. If they're of the same color, you add a blue ball to the bag. If they're of different colors, you add a red ball to the bag. (assume you have a big supply … [Continue reading]

## Calendar cube

A man has two cubes on his desk. Every day he arranges both cubes so that the front faces show the current day of the month. what numbers are on the faces of the cubes to allow this? … [Continue reading]

## Zeroes in 100 factorial

How many trailing zeroes are there in 100! (100 factorial) ? … [Continue reading]

## Average salary

Three coworkers would like to know their average salary. How can they do it, without disclosing their own salaries to other two? … [Continue reading]

## 100 doors

There are 100 doors, all closed. In a nearby cage are 100 monkeys. The first monkey is let out, and runs along the doors opening every one. The second monkey is then let out, and runs along the doors closing the 2nd, 4th, 6th,... all the … [Continue reading]

## Cube Puzzle

You have a normal six sided cube. I give you six different colors that you can paint each side of the cube with (one color to each side). How many different cubes can you make? Different means that the cubes can not be rotated so that they look … [Continue reading]