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 Marcello Pagano found that the birth weights of babies in the United States are not symmetric Care 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 u= 3432 g and standard deviation o = 482 g. The following questions refer to infants born from 37 to 43 weeks whose mothers did not have a history of diabetes.

 Compute the z-score of an infant who weighs 4289 g.  

Approximately what fraction of infants would you expect to have birth weights between 3020 g and 3350 g?  

Approximately what fraction of infants would you expect to have birth weights below 3020 g? 

A medical researcher wishes to study infants with high birth weights and seeks infants with birth weights among the heaviest 16%. Above what weight must an infant's birth weight be in order for the infant be included in the study?