chenni wrote:喝可口可樂的人占了75%,喝百事可樂的人占了35%請問同時喝可口可樂和百事可樂的人占了幾% Let A. and B. be people who drink Coca-Cola and Pepsi-Cola, respecyively.Assume that people either drink Coca-Cola or drink Pepsi-Cola;that is the probability of the union of A and B is 1, ie., P(A. U B.) = 1.SinceP(A. U B.) = P(A.) + P(B.) - P(A. B.) and P(A.) = .75 and P(B.) = .35,it yields P(A. B.) = .1.Hence the probability of people who drink both Coca-Cola and Pepsi-Cola is .1 (or 10%).