Suppose the mean income of firms in the industry for a year

Suppose the mean income of firms in the industry for a year is 100 million dollars with a standard deviation of 17 million dollars. If incomes for the industry are distributed normally, what is the probability that a randomly selected firm will earn between 115 and 128 million dollars? Round your answer to four decimal places.

Solution

Let X be the the income of firms in the industry for a year

Mean of x 100 and sigma =17

Required prob = P(115<x<128)

=P(0.88<z<1.65)

=0.4505 -0.3106

= 0.1399