Assume that the duration of human pregnancies can be described by a normal model with mean 266 days and standard deviation 16 days. a ) What percentage of pregnancies last between 260 and 280 days? b) At least how many days should the longest 10% of all pregnancies last? c ) Suppose a certain obstetrician is currently providing prenatal care to 40 pregnant women. Let Xrepresent the mean length of their pregnancies . According to the Central Limit Theorem, what's the distribution of this sample mean, Specify the model, mean, and standard deviation. d ) What's the probability that the mean duration of these patients pregnancies will be less than 260 days