A dishwasher has a mean lifetime of [mu] years with an estim…

A dishwasher has a mean lifetime of [mu] years with an estimated standard deviation of [s] years. The lifetime of a dishwasher is normally distributed. Suppose you are a manufacturer and you take a sample of [n] dishwashers that you made.  Find the probability that the sample would have a mean lifetime less than [xbar] years?