VG1
statistikk
Quiz
What is probability?
Probability tells us how likely something is to happen — from coin flips to weather forecasts and medicine.
What is probability?
A number between 0 and 1 that tells us how likely an event is:
- 0 = impossible
- 1 = certain
- 0.5 = fifty-fifty
The formula
P(A) = favourable outcomes / total possible outcomes
Example 1 — dice
P(6) = 1/6 ≈ 16.7%
(1 favourable out of 6 possible)
(1 favourable out of 6 possible)
Example 2 — coin flip
P(heads) = 1/2 = 50%
The complement rule
P(not A) = 1 - P(A)
P(not 6) = 1 - 1/6 = 5/6 ≈ 83.3%
Overview
| Event | P | Percent |
|---|---|---|
| Heads on a coin | 1/2 | 50% |
| 6 on a die | 1/6 | 16.7% |
| Hearts in cards | 1/4 | 25% |
| Even number on die | 1/2 | 50% |
Remember: Probability is always between 0 and 1. Never negative, never greater than 1!
Probability theory is nothing but common sense reduced to calculation.
— Pierre-Simon Laplace (1749–1827)
🧠 Test yourself
Question 1 of 3
What is P(even number) on a die?