4.6 A dishwasher has a mean lifetime of 5 years with an estimated standard deviation of 2 yea rs. The lifetime of a dishwashers is normally distributed. Suppose a bunch of samples taken, each sample has 10 dishwashers. a.) Find the standard deviation of the sample mean for dishwasher's lifetime. 1).) Find the probability that the sample mean of the dishwasher's lifetime will be greater than 6 years