1. The problem statement, all variables and given/known data It seemed much easier to screencap than to write out. 2. Relevant equations It helps to know that the number of states with speed between u and u+du is 2pi*u du 3. The attempt at a solution I've tried quite a few things but every time I get to trying to normalise I either get stuck integrating by parts over and over, or using http://en.wikipedia.org/wiki/Gaussian_integral<that, which doesn't arrive at the answer wanted. If someone could give me a push in the right direction it would be much appreciated.