问题
单项选择题
Each of the integers from 0 to 9, inclusive, is written on a separate slip of blank paper and the ten slips are dropped into a hat. If the slips are then drawn one at a time without replacement, how many must be drawn to ensure that the numbers on two of the slips drawn will have a sum of 10 ？（）
A．Three
B．Four
C．Five
D．Six
E．Seven
答案
参考答案：E
解析：
0到9的整数中，两个数相加其和为10的可能性有4种，即1+6，2+8，3+7，4+6，剩下0到5不可能与另一张纸条相加为10，要想确保抽出的纸条中有2张纸条上的数字相加为10，则必须抽7次。