Which of the following are probability distributions? Why?
(a)

Random Variable X ................ Probability
−2 .................................................... 0.1
−1 .................................................... 0.2
0 ...................................................... 0.3
1 ................................................... 0.25
2 .................................................... 0.15

(b)
Random Variable Y ......... Probability
1 ................................................. 1.1
1.5 ............................................. 0.2
2 ................................................. 0.3
2.5 ........................................... 0.25
3 ...........................................  –1.25
(c)
Random Variable Z ......... Probability
1 ........................................... 0.1
2 ........................................... 0.2
3 ........................................... 0.3
4 ........................................... 0.4
5 ........................................... 0.0