The second part of the TV sales problem requires calculation of the 90th percentile of the demand histogram. In mathematical notation, we are looking for a such that P(X>a)=.10. See Figure 4.4.
Example: To find the 90th percentile of TV sales, type the inputs (.90, 36, 8). The answer is 46.25, or approximately 46.
Exercise: Find the following percentiles for TV sales. Guess the percentile first, then use your calculator. Was your guess close?
a. 80th percentile
b. 20th percentile
c. 50th percentile