Probability Distribution Function (PDF) for a Discrete Random Variable · Exercise 18

Suppose that the PDF for the number of years it takes to earn a bachelor of science (B.S.) degree is given in.

$$\begin{array}{cc}\text{x}& \text{P(x)}\\ \text{3}& \text{.05}\\ \text{4}& \text{.40}\\ \text{5}& \text{.30}\\ \text{6}& \text{.15}\\ \text{7}& \text{.10}\end{array}$$

(a) In words, define the random variable X.
(b) What does it mean that the values 0, 1, and 2 are not included for x in the PDF?

Its source prints no answer for this problem, so there's nothing to check against.

OpenStax, Statistics · §4.1 Probability Distribution Function (PDF) for a Discrete Random Variable · Exercise 18