Posted by Anonymous on Tuesday, July 17, 2012 at 3:38pm.
You have two bags of marbles.
Bag 1 has 5 red and 6 blue marbles.
Bag 2 has 20 green and 5 red marbles.
What is the probability of drawing a red marble out of Bag 2, given that you drew a red marble out of Bag 1?

conditional probability  Ms. Sue, Tuesday, July 17, 2012 at 3:43pm
5/25 = 1/5
It makes no difference what color she drew from Bag 1.

conditional probability  MathMate, Tuesday, July 17, 2012 at 10:10pm
P(R1)=5/11
P(R2)=5/25
Since the drawing of the two bags are independent, we have
P(R1∩R2)=P(R1)*P(R2)
P(R2R1)=P(R2∩R1)/P(R1)
=P(R1)*P(R2)/P(R1)
=P(R2)
=1/5 as Ms.Sue had it.
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