ACT Preparation / Unit 15 ACT 1421 short lesson, about 20 seconds
Probability Basics
Captions available
The idea
When outcomes are equally likely, the probability of an event is the number of favorable outcomes over the total number of outcomes. Probabilities run from 0 to 1, and P(not A) = 1 − P(A).
In practice
Rolling a die, P(at least 5) = 2/6 = 1/3, so P(less than 5) = 2/3.
Where people slip
Count the whole sample space first.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Builds on
- Nothing. This is a starting point.
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