There are 12 marbles in the bag. When we first pick we have 4 blue marbles. So 4 blue marbles/12 random marbles. When we pick blue and noted, there are 3 marbles in the bag because of we didn't put it back. So when we choose again there are 11 marbles and 3 blue marbles in the bag. Choosing a blue one case is 3/11.
The last part of this case is happening as a chain. So we need to multiply our two answers.
