How about this.
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?
THE ANS : A>3/5
But how do you get those?