How about this.

Question

One bad contains 4 white balls and 6 black balls. Another bag contains 8 white balls and 2 black balls. A coin tossed to select a bad, then a ball is randomly selected from that bag.

a. What is the probability that a white ball will be drawn?
b. Suppose a white ball is drawn. What is the probability that it came from the First Bag?

Thanks

THE ANS : A>3/5
B>1/3

But how do you get those?

Answer 1

http://www.jiskha.com/display.cgi?id=1217983092

Use the ideas in Reiny's post; adjust for the numbers you're now posting.