Suppose that the weight W of male patients registered at a diet clinic has the normal distribution with mean 190 and variance 100.
a. For a random sample of patients of size n = 25, the expression P(< 180), in which  denotes the sample mean weight, is equivalent to saying P[Z > ?).
b. Find an interval {a, b) such that P{a <  < b) = .80 for the same random sample in part (a).