Service time for a customer coming through a checkout counter in a retail store is a random variable with the mean of 3.5 minutes and standard deviation of 4.0 minutes. suppose that the distribution of service time is fairly close to a normal distribution. suppose there are two counters in a store, n1=35 customers in the first line and n2=45 customers in the second line. find the probability that the difference between the mean service time for the shorter line x¯1 and the mean service time for the longer one x¯2 is more than 0.8 minutes. assume that the service times for each customer can be regarded as independent random variables.