Q: Two assembly lines I and II have the same rate of defectives in their production of voltage regulators. Five regulators are sampled from each line and tested. Among the total of ten tested regulators, four are defective. Find the probability that exactly two of the defective regulators came from line I.

So, I let N=10, n=5, and r=4 (defectives) and plugged these values into the hypergeometric distribution and got p(Y=2)=5/21.

Thus, I need to find P(Line I | y=2).

Am I on the right track or can this be made a lot easier?