AMC8 1994

AMC8 1994 · Q21

AMC8 1994 · Q21. It mainly tests Pigeonhole principle.

A gumball machine contains 9 red, 7 white, and 8 blue gumballs. The least number of gumballs a person must buy to be sure of getting four gumballs of the same color is

一个泡泡糖机里有9个红色的、7个白色的和8个蓝色的泡泡糖。一个人必须买至少多少个泡泡糖才能确保得到四个相同颜色的泡泡糖？

(A) 8 8

(B) 9 9

(D) 12 12

(E) 18 18

Answer

Correct choice: (C)

正确答案：（C）

Solution

Worst case: 3 each color=9, tenth forces 4 of one.

最坏情况：每种颜色各3个=9个，第十个将迫使某种颜色达到4个。

Topics

CP.005 Pigeonhole principle