A random sample of heat pumps of a certain type yielded the following observations on lifetime (in years):

2.0 1.3 6.0 1.9 5.1 .4 1.0 5.3 15.7 .7 4.8 .9 12.2 5.3 .6

a. Assume that the lifetime distribution is exponential and use an argument parallel to that of Example 7.5 to obtain a 95% CI for expected (true average) lifetime.

b. How should the interval of part

(a) be altered to achieve a confidence level of 99%?

c. What is a 95% CI for the standard deviation of the lifetime distribution? [Hint: What is the standard deviation of an exponential random variable?]