6) John wants to compare two means. His sample statistics were 16) X = 22.7, s,2 = 5.4, n, = 9 and 2 = 20.5, 5, = 3.6, 12 -9. Assuming equal variances, the pooled variance is: A) 4.9 B) 3.8 C) 5.1 D) 4.5 17) In a random sample of patient records in Cutter Memorial Hospital, six-month 17) B postoperative exams were given in 90 out of 200 prostatectomy patients, while in Paymor Hospital such exams were given in 110 out of 200 cases. In comparing these two proportions, normality of the difference may be assumed because: A) the samples are random, so the proportions are unbiased estimates. B) n7 2 10 and n(1 - 7) 2 10 for each sample taken separately. C) the probability of success can reasonably be assumed constant. D) the populations are large enough to be assumed normal