how to increase mathematical abillity

If one is too good, it doesn't necessarily means the other must be too. Maybe the other is good at Portuguese. I think that if he is average, that's already good. But, anyway, here goes my Tip: Teach him how to think. Math is not only knowleadge, it's about organizing your mind. If you teach him how to clean his mind, and organize his thoughs, he'll do math more quickly. Teach him a new way to count, a new way to make math. That'd help him. Hope I've helped.