In a clinical trial with overall survival as the primary endpoint, suppose that the patients' survival time follows an exponential distribution, T Exp() with S(t) = exp(t). Let 1 and 2 be the constant hazards for arms 1 and 2, respectively. We are interested in testing a one-sided hypothesis, H0 : 1 = 2 versus H1 : 1 > 2 (i) Compute the mean survival time, the median survival time, and the 75th per- centile of the survival time. (ii) Construct a Wald test statistic based on maximum likelihood estimators for testing H0, and determine the sample size formula. (iii) Suppose n1 = rn2, find the optimal r that minimizes the total sample size.