Question 1134973
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What is the probability that the first ball was blue, given that the second was red?<br>
That probability is<br><pre>
       P(1st was blue and 2nd is red)
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   P(2nd is red (and first was any color))<br></pre>
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:<br><pre>
A = P(1st red and 2nd red)
B = P(1st blue and 2nd red)
C = P(1st green and 2nd red)<br></pre>
Then the probability you are asked to find is {{{B/(A+B+C)}}}<br>
(Note that, in this problem, A = 0, because there is only 1 red ball in the box....)