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## Homework Statement

Bob has a marble sack with 20 marbles. 6 - purple, 8 - blue, 4 - white, 2 green.

If Bob randomly grabs 5 marbles what is the probability that at least 2 are purple and at least 2 are blue?

## Homework Equations

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## The Attempt at a Solution

I guess the part that is throwing me is taking one more than required. So lets say Bob only grabs 4 marbles. Would the probability be (6/20)*(5/19)*(8/18)*(7/17) = 14/969? If this is incorrect for picking 4 please explain as well. I would also appreciate it if you used the probability notation like p(b) as I need practice, but it is not necessary.This isn't for any math class, but a different subject. I've modified the problem, but the principle is the same. I don't have much background in probability (it has been 3 years since I've done some). What are some good resources for learning/relearning probability? I've been watching some videos on khanacademy.org.