We have 2 opaque bags, each containing 2 balls. One bag has 2 black balls and the other has a black ball and a white ball. You p
ick a bag at random and then pick one of the balls in that bag at random. When you look at the ball, it is black. You now pick the second ball from that same bag. What is the probability that this ball is also black?
Since we are trying to find the probability of 2nd being ball being black when we already know that first ball is black. This reduces our problem to probability by which we picked the bag with two black balls.
