(part 3)

c. Find the 90^th percentile. Draw a graph. Let k = the 90^th percentile.

$P(x<k)=(\text{base})(\text{height})=(k-0)(\frac{1}{15})$

$0.90=\left(k\right)\left(\frac{1}{15}\right)$

$k=(0.90)(15)=13.5$

k is sometimes called a critical value.

The 90^th percentile is 13.5 minutes. Ninety percent of the time, a person must wait at most 13.5 minutes.

Figure 5.16