David has two boxes containing shapes.

In box A there are 4 stars and 2 hearts.
In box B there are 2 stars and 1 heart.
David takes, at random, a shape from box A and puts it into box B.He then takes a shape from box B.
What is the probability that this shape is a star?

2 answers

Pr(star)= ((2+4/6)/(3+4/6))=2.666/3.666= .73
After the first transfer from A,
P(B=3stars, 1heart) = 2/3
P(B=2stars, 2hearts) = 1/3
So, the probability of getting a start when drawing from B is
2/3 * 3/4 + 1/3 * 1/2 = 2/3
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