Answer:
Suppose that the first die we roll comes up as a 1. The other die roll could be a 1, 2, 3, 4, 5, or 6. Now suppose that the first die is a 2. The other die roll again could be a 1, 2, 3, 4, 5, or 6. We have already found 12 potential outcomes, and have yet to exhaust all of the possibilities of the first die. But with a second dice, there will be 24 different possibilities.
Step-by-step explanation:
    1     2        3	4   5     6
1	(1, 1)   (1, 2)   (1, 3)   (1, 4)  (1, 5)   (1, 6)
2	(2, 1)   (2, 2)  (2, 3)  (2, 4)	(2, 5)  (2, 6)
3	(3, 1)   (3, 2)  (3, 3)  (3, 4)  (3, 5)  (3, 6)
4	(4, 1)   (4, 2)  (4, 3)  (4, 4)  (4, 5)  (4, 6)
5	(5, 1)   (5, 2)  (5, 3)  (5, 4)  (5, 5)  (5, 6)
6	(6, 1)   (6, 2)  (6, 3)  (<u>6, 4</u>)  (6, 5)  (6, 6)