one JJ math question...

redhat

34 . 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 sun of 10?

ANS.
E) 7

Could anybody figure out how to solve this question??[em14]
Thanx a lot![em09]

猫猫头

0，1，2，3，4，5，6
got it?

redhat

I was confused by the explanation:

0到9的整数有4种可能相加为10,即1+9, 2+8, 3+7, 4+6，剩下0和5不可能与另一张纸条相加为10，要想保证抽出的2张纸条上的数字相加为10则必须抽7次

...anyway, thanks!

猫猫头

我的做法是一种最小的可能性 就是从最小的开始 你会发现从0-5，其中任何两个想加都<10 所以一定要有7个数字

tongxun

redhat：这就是抽屉原理。