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Probability
A number between 0 and 1 that describes how likely something is. 0 means impossible, 1 means certain.
Roll & flip
Run hundreds of trials. Watch the experimental probability close in.
?
1
0
0%
2
0
0%
3
0
0%
4
0
0%
5
0
0%
6
0
0%
Theoretical: each face 16.67%. Total trials: 0.
Counting outcomes
When all outcomes are equally likely, probability is just a count:
P = (favourable outcomes) / (total outcomes)
Roll a fair die. P(rolling a 4) = 1/6. P(rolling an even number) = 3/6 = 1/2.
Probability scale
- 0 — impossible. (Rolling a 7 on a six-sided die.)
- 0.5 — fifty-fifty. (Heads on a coin.)
- 1 — certain. (Rolling a number from 1 to 6.)
Theory vs experiment
Theoretical probability comes from counting. Experimental probability comes from running trials and measuring. With more trials, experiment usually closes in on theory — but never perfectly. Try rolling 10 times, then 1000 times above.
Independent events
If two events don't affect each other (like two coin flips), you multiply their probabilities. P(two heads in a row) = 1/2 × 1/2 = 1/4.
The gambler's mistake
A coin doesn't remember. After 5 heads in a row, the next flip is still 50/50 — the coin doesn't owe you a tail.