The lengths of a particular animal's pregnancies are approximately normally distributed, with mean u = 267 days and standard deviation o = 12 days. (a) What proportion of pregnancies lasts more than 273 days? (b) What proportion of pregnancies lasts between 264 and 270 days? (c) What is the probability that a randomly selected pregnancy lasts no more than 255 days? (d) A "very preterm" baby is one whose gestation period is less than 237 days. Are very preterm babies unusual? 11 Click the icon to view a table of areas under the normal curve. (a) The proportion of pregnancies that last more than 273 days is (Round to four decimal places as needed.)