Question: A tetrahedron is a fully-symmetric pyramid-like solid, with four faces made up of equal-sized equilateral triangles. Suppose that the four faces contain different number of spots, from one spot to four spots, so that the tetrahedron may be rolled as a die. The number of spots which results from the roll of this die is the number of spots on the bottom face, the one which can not be seen. In the example, the die has thrown a two.

a. Suppose two such dice are rolled. Write a list of all possible equally-likely pairs of numbers of spots which could result.

b. If two such dice are rolled, what is the probability that the sum of the spots will be four?

c. If two such dice are rolled, what is the probability that the sum of the spots will be greater than two?