I'm guessing by standard gamma they mean the scale parameter (i.e. beta) is equal to 1. Since alpha = 2, we can just write down the density . You can solve for F(x) in the usual way using integration by parts. If you haven't had calculus, or are just being blindsided by this (since this is the pre-university forum), just post so and I'll give a different explanation (at some point, I have to go to class).