对于一道GWD DS题目标准答案的疑问

tangqi0652

If 2 different representatives are to be selected at random from a group of 10 employees and if p is the probability that both representatives selected will be women, is p >
1/2
(1)More than 1/2of the 10 employees are women.
(2)The probability that both representatives selected will be men is less than 1/10
.
A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.

这道题答案是E，可我觉得应该是B
因为可以推算出只有Women>=7开始，P才会大于1/2。所以条件1不充分，但是条件2说2次全选中men的概率Q小于1/10可以推出men<=3（因为men=3时，Q=1/15 < 1/10；men=4时，Q=2/15 > 1/10），间接推出Women>=7  then  >1/2

不知道我的理解是否正确，请各位大牛指教。

Gail小M

1) if there are N women
p=Cn2/C102=n(n-1)/90 if P>1/2   n(n-1) > 45 ,we can conclude that women should >7 (n=7 7*6=42<45)
thus1) insuff.

2) if there are m men
L=Cm2/C102=m(m-1)/90 if L<1/10   m(m-1)<9  men should <4 (<=3)  women >=7 insuff.

combine insuff.