service time for a customer coming through a checkout counter in a retail store is a random variable with the mean of minutes and standard deviation of minutes. suppose that the distribution of service time is fairly close to a normal distribution. suppose there are two counters in a store, customers in the first line and customers in the second line. find the probability that the difference between the mean service time for the shorter line and the mean service time for the longer one is more than minutes. assume that the service times for each customer can be regarded as independent random variables.