Unintended pregnancies. Birth certificates show that approximately 9% all births in the United States are to teen mothers (ages 15 to 19), 24% to young-adult mothers (age 20 to 24), and the remaining 67% to adult mothers (age 25 to 44). An extensive survey of live births examined pregnancy type, defining an unintended pregnancy as one that was unwanted or mistimed by at least two years. The survey found that “only 23% of births to teen mothers are intended, and 77% are unintended. Among births to young-adult women age 20–24, 50% are intended, and at ages 25–44, 75% are intended.”
a) Express all the percents cited here using probability notation, representing the sample space of live births in the United States.
b) What is the probability that any given live birth in the United States is unintended?