00:01
First, let's give a summary.
00:03
For arm a, there are six balls in total, and two of them are white.
00:08
For arm b, there are 12 balls and 8 of them are white.
00:14
And for arm c, there are four balls and one of them are white.
00:20
So what is the probability that exactly two white balls were selected? so there are three possibilities.
00:32
That is, the ball selected from a and b are white, and the ball selected from c are right.
00:49
So what is the probability? that is 2 over 6 times 8 over 12 times 3 over 4.
01:01
This equals 48 over 288.
01:08
So the second case is that the ball selected from the arm a and c are white and the ball selected from arm b are right.
01:23
So for this case, the probability is 2 over 6 times 4 over 12 times 1 over 4...