按双琴的话，得先补英文，再补数学

来源: 于 2020-05-19 10:30:05 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次

Bag A has 2 white marbles, Bag B contains 2 black marbles, Bag C contains one white marble and one black marble.

He picks a bag RANDOMLY and takes out ONE marble. It is a white marble.

the question

"What is the probability that the reamining marble from the same bag is also white?”

is the same question as:

"What is the probability that the first marble is from Bag A?"

.

end of story.

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