The manager of a cafeteria wants to estimate the mean time customers wait before served. A random sample of 49 customers has a mean waiting me of 8.4 minutes with a standard deviation of 3.5 minutes....

The manager of a cafeteria wants to estimate the mean time customers wait before served. A random sample of 49 customers has a mean waiting me of 8.4 minutes with a standard deviation of 3.5 minutes. Find a 90% confidence interval for the mean waiting time of all customers.