posted by Anonymous .
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?
5/25 = 1/5
It makes no difference what color she drew from Bag 1.
Since the drawing of the two bags are independent, we have
=1/5 as Ms.Sue had it.