求助一道数学题！

Radia_ting

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.3  b.4  c.5  d.6  e.7

dnsbind

7次吧，考虑最小概率，0，1，2，3，4，5，第七次才能满足条件

tongxiao88

选e:

极限情况为:5,6,7,8,9,0 were drawn,

必须再加上1,2,3,4其中之一,所以是7.

windlake

能再说说吗？

Economics

就是说当你从0到9取数时，如果开始取得数分别为：0，1，2，3，4，5的话，都无法保证其中有两个数和为10，但此时已取了6次，所以要想保证其中有两个数和为10，就至少要在取一次，也就是说只有你取七次时才能完全保证有两个数和为10.

Radia_ting

谢谢 ！！！！