The lengths of a particular animal's pregnancies are approximately normally distributed, with mean muequals262 days and standard deviation sigmaequals8 days. (a) What proportion of pregnancies lasts more than 276 days? (b) What proportion of pregnancies lasts between 256 and 264 days? (c) What is the probability that a randomly selected pregnancy lasts no more than 250 days? (d) A "very preterm" baby is one whose gestation period is less than 244 days. Are very preterm babies unusual?