Question 1134973: Assume that the box contains 9 balls: 1 red, 5 green, and 3 blue. Two balls are drawn at random, one after the other without replacement.
What is the probability that the first ball was blue, given that the second was red?
Found 2 solutions by greenestamps, ikleyn:
Answer by greenestamps(13200)   (Show Source):
You can put this solution on YOUR website!
What is the probability that the first ball was blue, given that the second was red?
That probability is
P(1st was blue and 2nd is red)
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P(2nd is red (and first was any color))
To find the answer, you need to find the probability that the second ball is red for all the different possibilities for the first ball:
A = P(1st red and 2nd red)
B = P(1st blue and 2nd red)
C = P(1st green and 2nd red)
Then the probability you are asked to find is 
(Note that, in this problem, A = 0, because there is only 1 red ball in the box....)
Answer by ikleyn(52781)  (Show Source):
You can put this solution on YOUR website! .
At given condition, first ball was drawn from the set (5 green and 3 blue).
Hence, the probability that the first ball was blue is  =  . ANSWER
Solved.
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