Question 1105385
Let be the events A: The picked person is a Girl.
                  B: the picked person is under 21 or 21.

First P(A) = 40%. P(B) = 80%.

a) P(A/B) = P(A&B)/P(B)=(90%(40%))/(80%)=9/20.
b) P(A^c&B) = 60%(80%) = 12/25.
c) P(B/A^c) = P(B&A^c)/P(A^c) = (12/25)/60% =4/5.

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