SAT and ACT math terms · SAT Math, ACT Math
Conditional probability
Conditional probability: The probability of an event given that another event has occurred, written P(A | B).
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What it means
P(A | B) = P(A and B) / P(B). In a two-way table, conditional probability means restricting attention to the row or column for the given condition.
Read carefully: the probability that a student plays a sport given they are a senior is different from the probability that a student is a senior given they play a sport.
Example
Of 80 seniors, 30 play a sport. The probability that a randomly chosen senior plays a sport is 30/80 = 0.375.
On the exam
Two-way tables with conditional probability questions are common on the SAT; the ACT also tests counting and probability.