Question

National Geographic still sells a considerable number of copies. Its demand for the April issue is forecasted to be normally distributed with a mean of 80 and a standard deviation of 35. If the Penn Bookstore stocks 100 copies, how many copies can they expect to return to the publisher at the end of the month

Answer 1

29

Explanation:

What we must do is calculate the z value for each value and thus find what percentage each represents and the subtraction would be the percentage between those two values.

We have that z is equal to:

z = (x - m) / (sd)

x is the value to evaluate, m the mean, sd the standard deviation

So for 100 copies we have:

z = (100 - 80) / (35)

z = 0.5714

and this value represents 0.7157

Which means, that of those 100 copies it is probable that they could be distributed:

100 * 0.7157 = 71.57

71 copies, so a total of about 29 (100 - 71) were being returned