posted by Katia .
my problem is:
From the box containing 5 red balls, 7 blue balls, 10 black balls. you select 4 balls
what is the probabilty that EXACTLY 2 balls are black.
i know that you start it/set it up like this:
c(10,2)c(2,1) divided by c(22,4)
and i can get the answer by plugging it in the calculator. but i would like to know how to solve it by hand. help?