Don't push him to be helped as he doesn't want it. Obviously he feels not as good as you at maths and his pride will not let him be humiliated by receiving help from you. The more you keep trying to help him the more humiliated he will feel. It doesn't matter if he could do better just let him do it by himself. You should not try and change your boyfriend you should accept him the way he is or you might find that your relationship will break up.