Answer
a. 0.705
b. 0.885
Work Step by Step
Given $\mu=19.32, \sigma=2.44$
a. A randomly selected year will have precipitation
greater than 18 inches for the first 7 months.
$z(18)=\frac{18-19.32}{2.44}=-0.54$
The probability for above z=-0.54 is 0.705
b. Five randomly selected years will have an average
precipitation greater than 18 inches for the first
7 months.
$z'(18)=\frac{18-19.32}{2.44/\sqrt 5}=-1.2$
The probability for above z'=-1.2 is 0.885
