Using all 1991 birth records in the computerized national birth certificate registry compiled by the National Center for Health Statistics (NCHS), statisticians Traci Clemons and Marcell° Pagano found that the birth weights of babies in the United States are not symmetric ("Arc babies normal?' The American Statistician, Nov 1999, 53:4). However, they also found that when infants born outside of the "typical" 37-43 weeks and infants born to mothers with a history of diabetes are excluded, the birth weights of the remaining infants do follow a Normal model with mean µ = 3432 g and standard deviation a = 482 g. The following questions refer to infants born from 37 to 43 weeks whose mothers did not have a history of diabetes.

a. Compute the z-score of an infant who weighs 3156 g. (Round your answer to two decimal places.) …………………?

b. Approximately what fraction of infants would you expect to have birth weights between 2150 g and 3980 g? (Express your answer as a decimal, not a percent, and round to three decimal places.) …………………?

c. Approximately what fraction of infants would you expect to have birth weights above 3980 g? (Express your answer as a decimal, not a percent, and round to three decimal places.) …………………?