Problema Solution
Twenty of the houses on a street receive cable t.v. and seven do not. A researcher studying the amount of time that people watch t.v. intends to visit five of the houses that receive cable t.v and two that do not. How many such selections of houses are there?
Answer provided by our tutors
C(20, 5)*C(7, 2) = (20!/(20 - 5)!5!)(7!/(7 - 2)!2!) = (16*17*18*19*20/120)(6*7/2) = 325,584 different selections.