Babies at Risk Weights of newborn babies in the United States are normally dis- tributed with a mean of 3420 g and a standard deviation of 495 g (based on data from "Birth Weight and Prenatal Mortality," by Wilcox et al., Journal of the American Medical Association, Vol. 273, No. 9).

a. A newborn weighing less than 2200 g is considered to be at risk, because the mor- tality rate for this group is at least 1%. What percentage of newborn babies are in the "at-risk" category? If the Chicago General Hospital has 900 births in a year, how many of those babies are in the "at-risk" category?

b. If we redefine a baby to be at risk if his or her birth weight is in the lowest 2%, find the weight that becomes the cutoff separating at-risk babies from those who are not at risk.

c. If 16 newborn babies are randomly selected, find the probability that their mean weight is greater than 3700 g.

d. If 49 newborn babies are randomly selected, find the probability that their mean weight is between 3300 g and 3700 g.