Statistics question.

Question

The lifetimes of a certain brand of battery have a mean of 45 hours and a

standard deviation of 18.

Find the probability that the mean lifetime of a random of such 50

batteries will be between 40 and 48 hours.

Answer 1

The mean will be normally distributed with mean = 45, standard deviation = 18 / √50

p ( 40 < mean < 48)

normalcdf

lower = 40

upper = 48

mean = 45

standard deviation= 18 / √50