Chapter 6.5, Problem 6.70ACB

Evaporation from swimming pools. Refer to the Heating/Piping/Air Conditioning Engineering (April 2013) study of evaporation from occupied swimming pools. Exercise 6.34 (p. 325). The researchers desired an estimate of the mean absolute value of the deviation between the actual and estimated evaporation level (recorded as a percentage). Using a small sample, the researchers obtained the following summary statistics for absolute deviation percentage $\bar{x}=18\%$, s = 20%. How many swimming pools must be sampled to estimate the true mean absolute deviation percentage to within 5% using a 90% confidence interval?