Draw marbles, spin spinners and roll dice. Learn how likely things are and write the chance as a fraction.
Start here. Probability is a number that tells us how likely something is. If it can never happen, it is impossible. If it always happens, it is certain. In between we say unlikely, even chance or likely.
Counting the chances. Put 3 red and 5 blue marbles in a bag and pick one without looking. There are 8 marbles, so 8 equally likely picks. 3 of them are red. The chance of red is 3 out of 8, written 3/8. The chance is always the number of ways you want, divided by the number of all possible ways.
Between 0 and 1. Impossible is 0, certain is 1, and an even chance is 1/2. The chances of all the colours in the bag add up to 1.
Experiment and theory. The theory tells you what should happen. An experiment shows what really happens. After 10 draws the results can be far from the theory. After 100 or 1000 draws they settle down and get close.
Two dice, two coins. To count outcomes, make a table. Two dice have 6 × 6 = 36 outcomes, and 6 of them add up to 7, so the chance of a sum of 7 is 6/36 = 1/6. Two coins have 4 outcomes: HH, HT, TH, TT.
Fair games. A game is fair when both players have the same chance of winning: an even chance, 1/2 each.
Try this above. In Play, put 1 red and 3 blue marbles in the bag, then press ×100. How close is red to 1/4? Now press it again and see what changes. Make red and blue equal and watch both bars.
Unlikely means it can happen, but the chance is less than one half. Likely means the chance is more than one half. Impossible means 0 and certain means 1.
No. A fair coin has no memory. Each flip is a new flip, and heads and tails are each an even chance, 1/2.
The draws in Play are random, just like real marbles. The theory stays the same, but the experiment changes each time. That is exactly what probability is about.
Pick the level, not the age. "Just starting" uses the words certain, likely and unlikely. "I know the basics" writes the chance as a fraction. "Challenge me" adds two dice, two coins, experiments and fair games.
No. It is free and needs no account. Your stars are saved in your own browser.