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3 colors of balls, blue,red and yellow, there are a large number of each color of balls which are distributed evenly. Ask what's the probability to get 3 balls which are all red color? What is probability to get 3 balls which are red, blue and yellow? Thanks

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Large number means that large that it (relatively almost) doesn't decrease when you substract one? – Rasmus Feb 15 '11 at 17:34
@Andy Leman: A tag (homework) would seem mandatory here. – Did Feb 15 '11 at 17:47
@Andy Leman: OK. Interview question before what? – Did Feb 15 '11 at 18:21
@Andy Leman: Shhh... Why get so emotional? :-) Bye. – Did Feb 15 '11 at 18:38
@Didier This particular user doesn't seem to be in the habit of asking well-formed questions, see, e.g., his Stack Overflow profile:… ...48 questions, 6 above +2 votes, 0 answers. For what it's worth, even if it wasn't a homework question, I thought he treated you quite rudely. – Uticensis Feb 15 '11 at 20:38

1 Answer 1

Hint 1: If the chance of pulling a red ball is 1/3, what is the chance of doing it three times in a row? Hint 2: What are the chances of pulling specifically a red ball first, a blue ball second, and a yellow ball third? How many different ways are there to get one of each in three draws?

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my answer is 1/27 for first one,right? ..I don't know second one. – Andy Leman Feb 15 '11 at 18:18
That's right. And the specific order RYB is the same, for the same reason, each pull is 1/3. But there are a number of ways to get one of each-you can read about permutations. Basically you have three choices for the first, two for the second, one for the third making six. You can list them by hand to see how it works. – Ross Millikan Feb 15 '11 at 18:37
Thank you Ross. really helpful – Andy Leman Feb 15 '11 at 18:39

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