Exercise 2 A random sample of n = 20 drill bits is used to put holes into a steel doorframe. The lifetime of a drill bit is measured as the number of holes drilled before the bit fails. The average...

Extracted text: Exercise 2 A random sample of n = 20 drill bits is used to put holes into a steel doorframe. The lifetime of a drill bit is measured as the number of holes drilled before the bit fails. The average lifetime of a drill bit is 12.68 holes with a known population standard deviation of 6.83 holes. (a) What is the population, the sample, the unit and the variable measured? (b) Using Minitab determine the 95% confidence interval for the true mean lifetime u of drill bits using the sample data.