A manufacturer claims that the average lifetime of its lightbulbs is equal to 36 months. A random sample of 64 bulbs has a mean lifetime of 32 months, and the sample standard deviation is 11 months. We will be using a z-test for the population mean at α = 0.05 to check the manufacturer’s claim.

The null hypothesis is:

H0: μ < 36

H0: μ > 36

H0: μ = 36

H0: μ ≠ 36