This question has been answered.
http://www.mathhelpforum.com/math-he...0986-help.html
There are three urns.
- The first contains 2 white and 4 black cards
- The second contains 8 white and four black cards
- The third contains 1 white and 3 black card.
If one card is selected from each urn, find the probability that exactly 2 white cards are drawn"
This question has been answered.
http://www.mathhelpforum.com/math-he...0986-help.html
What Plato is getting at is suppose the two white cards come from urns 1 and 2, repectively. Therefore, the third card, black, must come from urn 3.
So, (2/6)(8/12)(3/4)=1/6
Now, do the same for the other two cases and add them up. Supoose they come from urns 1 and 3 and urns 2 and 3