This week in school, there is a 75 percent probability of having a fire drill, a 50 percent probability of a tornado drill, and a 25 percent probability of having both drills. Let event F be a fire drill and event T be a tornado drill. Are the two events independent? No, because P(F ∩ T) ≠ P(F) • P(T). No, because P(F ∩ T) ≠ P(F) + P(T). Yes, because P(F ∩ T) = P(F) • P(T). Yes, because P(F) = P(T) + P(F ∩ T).
