Probability
Probability measures how likely an event is to occur, expressed as a number from 0 (impossible) to 1 (certain).
Basic Probability
P(event) = favorable outcomes / total outcomes
Rolling a 3 on a fair die: P = 1/6 ≈ 0.167 ≈ 16.7%
Drawing a red card from a deck: P = 26/52 = 1/2 = 50%
Theoretical vs Experimental
Theoretical: calculated from math (fair coins, dice).
Experimental: based on actual trials. As trials increase, experimental approaches theoretical.
Complementary Events
P(event NOT happening) = 1 − P(event)
If P(rain) = 0.3, then P(no rain) = 0.7
Compound Events
Independent events (one doesn't affect the other):
P(A and B) = P(A) × P(B)
Flipping heads twice: (1/2) × (1/2) = 1/4
FAQ
Can probability be greater than 1? No. Values range from 0 to 1 only.
What does P = 0.5 mean? The event is equally likely to happen or not.
Quick Quiz
Test what you just learned. Choose the best answer for each question.