The Payment Time CaseIt is concluded that confidence is 99% that µ ≤ 19.5 per day. If the population mean payment time is 19.5 days, the probability of observing a sample mean payment time of 65 invoices is less than or equal to 18.1077 days.Z value for 18.1077 is z = (18.1077-19.5)/0.5209 = -2.67 P (mean x <18.1077) = P (z < -2.67) =0.0038The TestA null hypothesis or (Ho) says the mean is greater than or equal to 19.5 days, whereas, the alternate hypothesis or (Ha) is less than 19.5[UCD18]. The ‘alpha’ is set at .05 because a 95% level of confidence is desired. The sample is greater than 30, therefore, the z test is used. The fdr discards the null if z is less than the critical value (CRV) of 1.645. This CRV is used for a one-tail test. The calculations follow:z=´x−µσ√n=18.11−19.54.2/√65=−1.390.520946=−2.67265The null is excluded because the result is z is -2.67, which is less than the CRV of 1.645. It is assumed that the new billing system creates a large reduction in paymenttime. The recommendation would be to continue with the new system across all other firms.