After transferring balls back and forth between two bags the probability of selecting a green ball from bag 2 is 3/5. How many green balls were in bag 2 at the outset?

Some relationships are transitive, such as `if A>B and B>C then it follows that A>C', but some are not. In a voting system, if A beats B and B beats C should we expect A to beat C?

Before a knockout tournament with 2^n players I pick two players. What is the probability that they have to play against each other at some point in the tournament?

Here are two games you have to pay to play. Which is the better bet?

These strange dice are rolled. What is the probability that the sum obtained is an odd number?

If everyone in your class picked a number from 1 to 225, do you think any two people would pick the same number?

Four cards are shuffled and placed into two piles of two. Starting with the first pile of cards - turn a card over... You win if all your cards end up in the trays before you run out of cards in. . . .

Two bags contain different numbers of red and blue marbles. A marble is removed from one of the bags. The marble is blue. What is the probability that it was removed from bag A?

A man went to Monte Carlo to try and make his fortune. Is his strategy a winning one?

"Statins cut the risks of heart attacks and strokes by 40%"

Should the Professor take statins? Can you help him decide?

If the score is 8-8 do I have more chance of winning if the winner is the first to reach 9 points or the first to reach 10 points?

It is believed that weaker snooker players have a better chance of winning matches over eleven frames (i.e. first to win 6 frames) than they do over fifteen frames. Is this true?

Newspapers said that eating a bacon sandwich every day raises the risk of bowel cancer by 20%. Should you be concerned?

A gambler bets half the money in his pocket on the toss of a coin, winning an equal amount for a head and losing his money if the result is a tail. After 2n plays he has won exactly n times. Has. . . .

Can you devise a fair scoring system when dice land edge-up or corner-up?

Use this animation to experiment with lotteries. Choose how many balls to match, how many are in the carousel, and how many draws to make at once.

A player has probability 0.4 of winning a single game. What is his probability of winning a 'best of 15 games' tournament?

This article, for students and teachers, is mainly about probability, the mathematical way of looking at random chance.

How can we find out answers to questions like this if people often lie?

You have two bags, four red balls and four white balls. You must put all the balls in the bags although you are allowed to have one bag empty. How should you distribute the balls between the two. . . .

Explore the distribution of molecular masses for various hydrocarbons

Investigate the molecular masses in this sequence of molecules and deduce which molecule has been analysed in the mass spectrometer.