Jack wants to send thank you cards to everyone who got him a gift for his wedding. He sent out 200 invitations. 90% of people RSVPed but only 80% of people who RSVPed actually showed up. Then 10 people who showed up didn't get a gift. How many thank you cards does he need? Give me reasons, before answering the question
He got 200 * .9 = 180 RSVP. Of those only 180 * .8 = 144 people showed up. So only 144 - 10 = 134 got him gifts and hence need thank you cards. So the final answer is 134.