16 or more books sold in a day will include two intervals from the given table:
a) 16 - 20 books sold.
Probability = 0.201
b) 21 - 25 books sold.
Probability = ?
Since the table gives the probability distribution, the sum of all the probabilities must be equal to 1. We are given the probabilities of 4 out 5 intervals. So in order to find the probability of the 5th interval (21-25) we can subtract the sum of probabilities of rest of the intervals from 1.
So, P(21 - 25) = 0.019
In order to find the probability of 16 or more books sold we need to sum the probabilities of both these intervals.
So, the probability of 16 or more books being sold on a given day = 0.201 + 0.019 = 0.220
