1. assume that the probability of conception in any given month among sexually active couples not practicing birth control is constant at 0.20 per month, independent of the number of months the couple has been active. what is the expected waiting time to first birth?

2. a college is planning to subject admitted freshman to " At home test kit for illicit drugs", which has been shown to be fairly reliable, in the sense that 90% of those using drugs test positive, while only 10% of those not using drugs test positive (in your age group). Assume that 20% of the population in your age group actually use illicit drugs. Alas, you test positive. What is the probability that you are truly and fairly busted? What's your probability of using illicit drug without knowing anything else about you ?