More light bulbs: Someone claims to have developed a new lightbulb whose mean lifetime is 1800 hours with a standard deviation of 100 hours. A sample of 100 of these bulbs is tested. The sample mean lifetime is 1770 hours.
a. If the claim is true, what is the probability of obtaining a sample mean that is less than or equal to 1770 hours?
b. If the claim is true, would it be unusual to obtain a sample mean that is less than or equal to 1770 hours?