Question

An amusement park reports that the probability of a visitor riding its largest roller coaster is 30 percent, the probability of a visitor riding its smallest roller coaster is 20 percent, and the probability of a visitor riding both roller coasters is 15 percent.

Which equation can be used to calculate the probability of a visitor riding the largest or the smallest roller coaster?

P(largest or smallest) = 0.30 - 0.20
P(largest or smallest) = 0.30 + 0.15 - 0.20
P(largest or smallest) = 0.30 + 0.20 - 0.15
P(largest or smallest) = 0.30 + 0.20

Answer 1

Use inclusion–exclusion: P(A ∪ B) = P(A) + P(B) − P(A ∩ B).
So P(largest or smallest) = 0.30 + 0.20 − 0.15 = 0.35 (35%).