Suppose the length of time a person takes to use an ATM machine is normally distributed with mean μ = 100 seconds and standard deviation σ = 10 seconds. There are n = 4 people ahead of Jackson in a line of people waiting to use the machine. He is concerned about T = total time the four people will take to use the machine.
a. What is the mean value of T = total time for the four people ahead of Jackson?
b. Assuming that the times for the four people are independent of each other, determine the standard deviation of T.