Verify whether or not each of the following is a probability function. State your conclusion and explain.

Question:

Verify whether or not each of the following is a probability function. State your conclusion and explain.
a. f (x) = 3x/8x for x _ 1, 2, 3, 4
b. f (x) _ 0.125, for x _ 0, 1, 2, 3 and f (x) _ 0.25, for x _ 4, 5
c. f (x) _ (7 - x)/28, for x _ 0, 1, 2, 3, 4, 5, 6, 7
d. f (x) _ (x2 + 1)/60, for x _ 0, 1, 2, 3, 4, 5