1. Of the PhD's in mathematics/statistics awarded to US citizens, about 35% are earned by women. Suppose a sample of 400 mathematics/statistics PhD's is taken.
(a) How many in the sample are expected to be men? Answer: 260
(b) What is the probability that at least 140 are women? Answer: 1/2
(c) What is the probability that fewer than 200 are men? Answer: about 0 (5.6.9)
(a) How many in the sample are expected to be men? Answer: 260
0.65 * 400 = 260
(b) What is the probability that at least 140 are women? Answer: 1/2
z = (140 - 140)/0.35 * 0.65 * 400 = 0
P(z > 0) = 0.5 = 1/2
(c) What is the probability that fewer than 200 are men? Answer: about 0 (5.6.9)
z = (200 - 260)/0.35 * 0.65 * 400 = -6.29
P(z < -6.29) = 0
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