Probability — Favorable Over Total

Basic formula: P(event) = favorable outcomes / total outcomes

Two-way tables: The SAT's favorite probability format.

"Given that a student is female, what is the probability she plays soccer?"

Look ONLY at the female row. Soccer females / total females.

And vs Or:

P(A and B) = P(A) x P(B) for independent events

P(A or B) = P(A) + P(B) - P(A and B)

Conditional probability: "Given that X happened, what is the probability of Y?"

Restrict your total to only the X group. Then find Y within that group.

Strategy: Always identify the denominator first. "Out of what group?" determines your total.

Reference:

Wikipedia: Probability

https://en.wikipedia.org/wiki/Probability