In a large group of Americans in 2001-2002, the probability of visiting a doctor's office in the past 12 months was 0.8.
a. For two randomly chosen Americans in 2001-2002, what is the probability of at least one of them (either the first and not the second, or the second and not the first, or both) visiting a doctor that year?
b. Show how to get the answer to part (a) by subtracting from 1 the probability that neither of them visits a doctor.