Well, he has a 4/6 or 2/3 chance of pulling a green marble. Drawing a second marble would make it another 2/3 chance. So he would have a 4/6 chance since 2/3 + 2/3 = 4/6.
The probability of drawing two green marbles in a row is 12/30, this is because when you draw the first green marble, you are losing a marble, so after that, the chances of drawing a green marble is smaller.
