Probability
Calculate probability of events and combinations
How to use Probability
- 1Choose the probability scenario (single event, two events, or combinations).
- 2Enter the numbers of favorable and total outcomes.
- 3Read the probability as a fraction, decimal, and percentage.
Understanding Probability
P = Favorable outcomes / Total outcomesProbability quantifies how likely an event is, from 0 (impossible) to 1 (certain). It is the ratio of favorable outcomes to all possible outcomes.
It underpins games of chance, risk assessment, quality control, and any decision made under uncertainty.
Frequently asked questions
What does a probability of 0.5 mean?
It means the event is as likely to happen as not — a 50% chance, like a fair coin landing heads.
How is probability written?
As a fraction, a decimal between 0 and 1, or a percentage between 0% and 100%.
Can probabilities be added?
Only for mutually exclusive events. Otherwise you must account for overlap to avoid double-counting.