Ok so you have it now. What I was trying to get you to do was:
the ">=" was the sticking point that you'd missed.
I'm not sure why your original code failed, as I said earlier. I can only assume that case had the *exact* number of points necessary to get the prize, and somehow a rounding error wheb dividing worked its way in. I couldn't find an example to demonstrate it though.
(a/12)//b>0 would fail, whereas (a/12)>=b would work.