Question: The length of time (in days) between the billing and the receipt of payment was recorded for 15 randomly selected clients of the legal firms for accounts X, Y and Z. Assume the normally distributed time between the billing and the receipt of payment!

X: 5 6 5 7 6 4 4 5 5 5 5 5 5 5 6

Y: 7 10 7 8 6 8 6 8 10 7 6 7 7 6 8

Z: 4 3 5 5 4 3 3 5 5 4 6 3 2 3 4

a) Calculate and interpret 99% confidence intervals for the mean time between billing and receipt of payment for all firm’s accounts!

b) Do the same thing also for the population dispersion and standard deviation!