You test 20 components for 30 hours. Failures were recorded at the following times (units are in hours) 0.32 2.8 25.7 28.9

a) Give the point estimate of the failure rate, and the corresponding MTTF.

b) Give a 95% confidence interval for the true failure rate.

c) Suppose you need to be 95% confident that the true failure rate is < 0.018 hours-1. What is the maximum failure rate you could have estimated in part a), assuming that there were four failures?

d) Imagine you were planning this experiment. You have 20 components and have decided to test for 30 hours. What is the maximum number of failures that would be allowable, given that you want to be 95% confident that the true failure rate is < 0.018 hours-1?