Probability Calculator
The Probability Calculator converts favorable outcomes out of a total into a probability — shown as a percentage, a decimal and a simplified fraction, such as 2/5 or 40%.
What this means
Probability measures how likely an event is, from 0 (impossible) to 1 (certain). If 2 of 5 outcomes are favorable, the probability is 2/5, which is 0.4 or 40%.
How we calculate it
Formula
P = favorable ÷ total. Shown as a percentage (P × 100) and a simplified fraction.Worked example
2 favorable outcomes out of 5:
- 1Probability = 2 ÷ 5 = 0.4
- 2As a percentage: 0.4 × 100 = 40%
- 3As a fraction: 2/5
Important assumptions
- All outcomes are assumed equally likely.
- Favorable outcomes cannot exceed the total.
Frequently asked questions
What is the probability of an event that always happens?
1, or 100%. An impossible event has probability 0, or 0%.
How do I convert a fraction to a probability percent?
Divide the numerator by the denominator and multiply by 100. For 3/4, that is 0.75 × 100 = 75%.
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