Game Ideas

I'm working today on coming up with a pitch to make to the class tomorrow. I'm finding that my main problem is with keeping the scope small. Every time I think of some cool idea and run with it for a while, it seems to end up practically turning into a game of its own. Anyway, I'd like to do an educational game for kids using addition, subtraction, and multiplication. Of course there are already games like this, but they aren't necessarily the most fun. I'd like to make something where the math is there and is still intrinsic to the gameplay, but is perhaps not thrown in your face so bluntly. I'm thinking along the lines of using equations to fight monsters. The character will start out only able to load one operation into his "gun" at a time, and will only possess the number "1" as ammo. As he grows and/or neutralizes monsters, the gun will level up, accept higher numbers, and will gain the ability to chain more operations. An added element will be the ability to upgrade your weapon with rare pieces gained from monsters by dispatching them with fewer operations. We could do something fun with prime monsters. :)