Posted by
**Stuck** on
.

"In vase A, there are 3 red balls and 5 white balls. In vase B, there are 6 red balls and 4 white balls. Two balls are to be drawn at random, without replacement, from each vase. What is the probability of selecting 4 red balls?"

(Answer: 1/28)

So I thought about doing 4 cases and then adding them up (don't pick red ball in A, don't pick red ball in B...pick red ball in A, pick red ball in B...etc...).

I did this:

(3/8)(3/7)(6/10)(6/9) +

(3/8)(2/7)(6/10)(5/9) +

.....

But it doesn't work. What am I doing wrong?