Posted by **Emily** on Tuesday, December 7, 2010 at 5:11pm.

An Urn contains 7 red and 3 white balls. Two balls are drawn in succession without replacement. If the second ball is white, what is the probability that the first ball was white?

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**PsyDAG**, Tuesday, December 7, 2010 at 11:37pm
It doesn't matter what the second ball is. Since no balls have been drawn before the first ball, probability = 3/10.

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**lanya**, Wednesday, July 1, 2015 at 10:47am
A box contain 3 red balls and 6 white balls. One ball was pulled and was seen its collar, and after that was pulled another ball.Find the probability that the first ball was white and the second was red ?

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