A box contains 3 red and 7 blue pens. Two pens are drawn one after the other without replacement. Given that the first pen drawn is red, what is the probability that the second pen is also red?

Question

Accepted Answer

2/9. After a red pen is removed, 9 pens remain of which 2 are red, so the conditional probability is 2/9. The value 1/15 answers a different question — the probability that both pens are red, (3/10)(2/9).

A box contains 3 red and 7 blue pens. Two pens are drawn one after the other without replacement. Given that the first pen drawn is red, what is the probability that the second pen is also red?

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