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July 14th 2005, 01:37 PM
Can anyone out there help me understand the explanation of Problem Set # 3, question 4 from the ACTEX manual (pg. 79)? Thanks.

robertr24
July 18th 2005, 12:34 AM
They're asking for the probability of 1 red and 2 white balls, given that there are AT LEAST 2 white balls. So out of the two given possibilities of either 2 white balls OR 3 white balls, what's the probability of 2? You have to take the probability of getting 2 white balls and 1 red ball and divide it by the probability of all the given scenarios happening, which is either 2 white balls or 3 white balls. If you're choosing 3 balls out of 10 (6 white, 4 red), then the probability of getting 2 white and 1 red is 6 "choose" 2 multiplied by 4 "choose" 1. Go back to pg 73 and give the "combinations" part another couple of reads. When I was first learning this stuff a few months ago, I had to read these sections like eight times to understand it. I hope that helps. Good luck.