Question

For a population mean: Assume a motor uses an average of 138 kw hours per year. If a random sample of 14 motors found that the motor used an average of 147 kilowatt hours per year with a standard deviation of 13.2 kilowatt hours, does this suggest at the α = 0.05 level of significance that this type of motor uses on average more than 138 kilowatt hours annually? Assume the population of kilowatt hours to be normal. Show work.

A turbine lasts on average 4,000 hours. A random sample of 25 turbines found the mean lifetime to be 3,890 hours. If the population standard deviation is known to be 80 hours, is there enough evidence, at the α=0.05 significance level,
to show the mean lifetime is not 4000 hours?

A coldpack will have a mean lifetime of 4 hours. A random sample of 35 coldpacks found the mean lifetime to be 3.91 hours. If the population standard deviation is known to be 0.22 hours, is there enough evidence at the α=0.05 significance level, to show the mean lifetime is less than 4 hours?

Answer 1