Chapter 5.3, Problem 2CS

CASE STUDY Birth Weights in America

The National Center for Health Statistics (NCHS) keeps records of many health-related aspects of people, including the birth weights of all babies born in the United States.

The birth weight of a baby is related to its gestation period (the time between conception and birth). For a given gestation period, the birth weights can be approximated by a normal distribution. The means and standard deviations of the birth weights for various gestation periods are shown in the table below.

One of the many goals of the NCHS is to reduce the percentage of babies born with low birth weights. The figure below shows the percents of preterm births and low birth weights from 2007 to 2015.

2. What percent of the babies born within each gestation period have a low birth weight (under 5.5 pounds)?

1. (a) 28 to 31 weeks
2. (b) 32 to 33 weeks
3. (c) 39 to 40 weeks
4. (d) 42 weeks and over