8. The mean running time of a certain variety of nickel-cadmium rechargeable flashlight battery is known to be normally distributed with a mean of 8.5. A change in production method for this
battery has been proposed, and a simple random sample of 64 batteries produced by the new
method has mean running time of 8.72 hours. Assume the population is normally distributed with
a standard deviation of 0.55 hour as known and remains unchanged, test a claim that the new
production method improving the battery mean running time using 0.05 significance level.