a fraction is a part of a whole, right? So which part of what whole are we looking for?
 LOL good question. Total KE?? But what is the total kineteci eenrgy here is it KE rot+ KE trans?? so is 1/2mv^2/1/2mv^2+1/5mv^2?
 Ke rot /KEtotal??? Is it like this 1/2mv^2/1/2mv^2+1/5mv^2?
 it actually tells you in the question ;) "What fraction of its kinetic energy is rotational?" in other words: Which part of the total kinetic energy is rotational kinetic energy? Thus, we are looking for the rotational part of the total kinetic energy. if you have $\frac{\frac{1}{2}mv^{2}}{\frac{1}{2}mv^{2}+\frac{1}{5}mv^{2}}$ then what is that representing?
 a fraction .... but if the m's and v's cancel they give 5/7 not 2/7 i give up.
 wait! don't give up! we're almost there :D what I was just asking was what's on top? Is it rotational kinetic energy or tangential kinetic energy?
 KE rot
 is $\frac{1}{2}mv^{2}$ the rotational kinetic energy?
 ahh tangential is 1/2mv^2 my bad KE rot is 1/5Iw^2? ARRGHHH JFC!!! ROFLMAO!!! I though KE rot was 1/2mv^2 when is 1/5mv^2 now it does give 2/7!! :P Thank you so much for your patients dude!!!
 no problem, glad I could help :)