"In Problems 17–20, determine whether or not the histogram indicates that a normal distribution could be used as a model for the variable.
Length of Phone Calls The relative frequency histogram represents the length of phone calls on my wife’s cell phone during the month of September. "

"In Problems 17–20, determine whether or not the histogram indicates that a normal distribution could be used as a model for the variable.

Birth Weights The relative frequency histogram represents the birth weights (in grams) of babies whose term was 36 weeks. "

In Section 10.2, we tested hypotheses regarding a population proportion using a z-test. However, we can also use the chi-square goodness-of-fit test to test hypotheses with k = 2 possible outcomes. In Problems 25 and 26, we test hypotheses with the use of both methods.

Low Birth Weight According to the U.S. Census Bureau, 7.1% of all babies born are of low birth weight . An obstetrician wanted to know whether mothers between the ages of 35 and 39 years give birth to a higher percentage of low-birth-weight babies. She randomly selected 240 births for which the mother was 35 to 39 years old and found 22 low-birth-weight babies.

a. If the proportion of low-birth-weight babies for mothers in this age group is 0.071, compute the expected number of low-birth-weight births to 35- to 39-year-old mothers. What is the expected number of births to mothers 35 to 39 years old that are not low birth weight?