Answer:
a. 3 ways: -3 and -1; -2 and -2; -1 and -3
b. 5 ways: -2 and 2; -1 and 1; 0 and 0; 1 and -1; 2 and -2
c. 6 ways: -3 and 2; -2 and 1; -1 and 0; 0 and -1; 1 and -2; 2 and -3
d. A sum of -1 would (probabilistically) be the most popular. There are 36 (6 x 6) possible outcomes every time you roll two 6-sided dice. In this case, the possible outcomes are:
-6: 1 way
-5: 2 ways
-4: 3 ways
-3: 4 ways
-2: 5 ways
-1: 6 ways
0: 5 ways
1: 4 ways
2: 3 ways
3: 2 ways
4: 1 way
So -1 is the most likely sum since it can be rolled 6 different ways, which is more ways than any other sum. A sum of -1 will be rolled 6/36 (or 1/6) of the time.