The life in hours of a 75-watt light bulb is known to be approximately normally distributed, with standard deviation = 25 hours. A random sample of 20 bulbs has a mean life of = 1014 hours.

(a) Is this sufficient evidence to support the claim that bulb life exceeds 1000 hr? Use = 0.05.

b) What is the P-value for the test in part (a)?

(c) Construct a 95% two-sided confidence interval on the mean life.