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A box contains 4 white balls and 3 red balls. In succession, two balls are randomly selected and removed from the box. Given that the first removed ball is white, the probability that the second removed ball is red is

1. 1/3
2. 3/7
3. 1/2
4. 4/7

Correct answer: 1/2

Solution

Given the first ball drawn is white, the box has 3 white and 3 red left (6 total). P(second is red)=3/6=1/2. Stored answer 3/7 is wrong; correct is 1/2.

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