The time spent by a customer at a checkout counter has mean 4 minutes and standard deviation 2 minutes. a) What is the probability that the total time taken by a random sample of 50 customers is less...

The time spent by a customer at a checkout counter has mean 4 minutes and standard deviation 2 minutes. a) What is the probability that the total time taken by a random sample of 50 customers is less than 180 minutes? b) Find the 30th percentile of the total time taken by 50 customers.