Derived Distribution
Compose one or more simple random variables to get more complicated r.v. (This is how we go from simple model to complicated model) ($f(X)$)
Discrete
Obvious formula
$$
P_Y(y) = P(Y=y) = \sum_{\text{all x if g(x)=y}} P_X(x)
$$
$$
P_Y(4) = P_X(5)+P_X(4) = 0.4 + 0.3 = 0.7
$$
Linear Example
