A box contains 5 white balls and 6 black balls. Two balls are drawn out of the box at random. What is the probability that they both are white?
5 + 6 means there are 11 balls in total.
Of these 11, 5 are white, so the probability of the first ball that's drawn being white is 5/11.
I'll assume the ball isn't put back into the box. So now you have 10 balls left, 4 of which are white.
('cause you already removed one white ball, the total number of balls and the number of white balls goes down)
Which means that the second pull has a 4/10 chance of being a white ball.
Both of these events need to happen, so you multiply the chances:
(5/11) * (4/10) = 2/11
