PUMaC 2015 · 团队赛 · 第 2 题

PUMaC 2015 — Team Round — Problem 2

[ 2 ] Sally is going shopping for stuffed tigers. She finds 5 orange, 10 white, and 2 cinnamon colored tigers. Sally decides to buy two tigers of different colors. Assuming all the tigers are distinct, in how many ways can she choose two tigers?

解析

[ 2 ] Sally is going shopping for stuffed tigers. She finds 5 orange, 10 white, and 2 cinnamon colored tigers. Sally decides to buy two tigers of different colors. Assuming all the tigers are distinct, in how many ways can she choose two tigers? Solution: She can choose to buy three different combinations of colors. • Sally can buy 5 · 10 different combinations of orange and white. • Sally can buy 5 · 2 different combinations of orange and cinnamon. • Sally can buy 10 · 2 different combinations of white and cinnamon. Therefore there are 50 + 10 + 20 = 80 ways. Author: Heesu Hwang