Definition: Probability is a number from 0 to 1 that measures how likely an event is to happen, with 0 meaning impossible and 1 meaning certain.
What is probability?
Probability measures chance. It is written as a fraction, decimal, or percent between 0 and 1, or 0 and 100 percent.
How do you compute it?
When outcomes are equally likely, P(event) = favorable outcomes / total outcomes. A drawer holds 5 red, 7 blue, and 8 green socks. The chance of a blue sock is 7 / 20, which is 0.35 or 35 percent.
What does the scale mean?
- 0: impossible
- Near 0: unlikely
- 0.5: even chance
- Near 1: likely
- 1: certain
What is the complement?
The probability that an event does not happen is 1 minus its probability. The chance of not blue is 1 – 7/20 = 13/20.
How do you interpret it?
A probability of 0.35 does not promise 7 blue socks in 20 tries. It describes long-run behavior across many repeats.
What is a common mistake?
Believing in a streak. If Mathbot flips heads four times in a row, the next flip is still 50 percent heads.