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 (“Are 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 σ = 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 4804 g. (Round your
answer to two decimal places.)
Approximately what fraction of infants would you expect to have
birth weights between 2640 g and 3900 g? (Express your answer as a
decimal, not a percent, and round to three decimal places.)
Approximately what fraction of infants would you expect to have
birth weights above 3900 g? (Express your answer as a decimal, not
a percent, and round to three decimal places.)
A medical researcher wishes to study infants with low birth weights
and seeks infants with birth weights among the lowest 2%. Below
what weight must an infant's birth weight be in order for the
infant be included in the study? (Round your answer to the nearest
gram.)
g
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