Posted by Katia on Monday, December 13, 2010 at 7:34pm.
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.
so i know how to start it
c(10,2)c(2,1)

c(22,40
but how do you solve that ?

Math  Katia, Monday, December 13, 2010 at 7:35pm
i meant c(10,2)c(2,1) divided by c(22,4)

Math  Reiny, Monday, December 13, 2010 at 9:48pm
so we want 2 from the black, then 2 more from the rest
prob of that = C(10,2) C(12,2) / C(22,4)
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