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.