Thread: probability generating function

Let Y=x+4. Compute rY(t) in terms of rX

is the answer just

r 3X+4 (t)

?

you mean y = 3x+4

then ry(t) = E(t^y)

so E(t^y) = E(t^3x+4)

=E(t^3x * t^4)

=t^4 + E(t^3x)

=t^4 + rx(t^3)