a)How many cards must be selected from a standard deck of 52 cards to guarantee that at least three

题目

a)How many cards must be selected from a standard deck of 52 cards to guarantee that at least three cards of the same suit are chosen?
b)How many must be selected to guarantee that at least three hearts are selected?

答案

抽屉原理及最差原则
建立抽屉,4种花色看做4个抽屉,考虑最差情况：
（1）前8张,每种花色各两张
那么再抽出任意一张,前面8张中肯定与这张花色相同
即至少要抽出8+1=9张
（2）黑桃占13张,红桃占13张,其余的占26张,所以至少要取26+3=29张