86.

a. In Exercise 82, what is the median lifetime of such tubes? [Hint: Use Expression (4.12).]

b. In Exercise 84, what is the median return time?

c. If X has a Weibull distribution with the cdf from Expression (4.12), obtain a general expression for the (100p)th percentile of the distribution.

d. In Exercise 84, the company wants to refuse to accept returns after t weeks. For what value of t will only 10% of all returns be refused?