I have this question from my textbook I'm not sure how to answer. I got the first part but the second part is a bit confusing.
It goes something like this:
"Two percent of the population has a certain condition for which there are two diagnostic tests. Test A which costs \$1 per person, gives positive results for 80% of persons with the condition and for 5% of persons without the condition. Test B, which costs $100 per person , gives positive results for all persons with the condition and negative results for all persons without it."
Suppose that 2000 persons are given test A, and then only those who test positive are given test B. Show that the expected cost is \$15,000 and the expected number of cases. I know the expected value of random variable X is defined as: $$E[X]=x_1p_1 + x_2p_2\dots+x_kp_k$$