The document discusses three probability applications: 1) The probability of having 0, 1, 2, etc. boys before the first girl for a couple planning children. 2) The probability that the first, second, etc. anti-depressant drug tried is effective for a newly diagnosed patient, given a 60% effectiveness rate. 3) The expected number of donors that need to be tested to find a matching kidney donor for transplant, given a 10% probability of a random donor being a match.