From a random sample of size 12 from a normal distribution, one has calculated the 95% confidence interval for y and obtained the result (18.6, 26.2). (a) Calculate the sample mean and variance. (b) Also calculate the 99% confidence interval for M. () Without calculating the critical region of P-value, can you reach a conclusion for testing the livo hypotheses 0) Ho: HI = 20 vs Ha: M /= 20, and (il) Ho: I = 18 vs Ha: I /= 18