# Twins Twins are often born after a pregnancy that lastsless than 9 months. On the next page is a graph from theJournal of the American Medical Association (JAMA)showing the rate of preterm twin births in the United States over the past 20 years. In this study, JAMA catego-rized mothers by the level of prenatal medical care they received: inadequate, adequate, or intensive.a) Describe the overall trend in preterm twin births. b) Describe any differences you see in this trend, depend-ing on the level of prenatal medical care the mother received.c) Should expectant mothers be advised to cut back onthe level of medical care they seek in the hope ofavoiding preterm births? Explain.a) Create a linear model and predict the number ofgallons that will be available in 2005.b) The exam then asked students to estimate the yearwhen leaded gasoline will first become unavailable,expecting them to use the model from part a to answerthe question. Explain why that method is incorrect.c) Create a model that would be appropriate for that task,and make the estimate.d) The “wrong” answer from the other model is fairlyaccurate in this case. Why?

Question
Twins Twins are often born after a pregnancy that lasts
less than 9 months. On the next page is a graph from the
Journal of the American Medical Association (JAMA)
showing the rate of preterm twin births in the United
States over the past 20 years. In this study, JAMA catego-
rized mothers by the level of prenatal medical care they
a) Describe the overall trend in preterm twin births.
b) Describe any differences you see in this trend, depend-
ing on the level of prenatal medical care the mother
c) Should expectant mothers be advised to cut back on
the level of medical care they seek in the hope of
avoiding preterm births? Explain.a) Create a linear model and predict the number of
gallons that will be available in 2005.
b) The exam then asked students to estimate the year
when leaded gasoline will first become unavailable,
expecting them to use the model from part a to answer
the question. Explain why that method is incorrect.
c) Create a model that would be appropriate for that task,
and make the estimate.
d) The “wrong” answer from the other model is fairly
accurate in this case. Why?