I would start with number theory and getting very good at managing numbers in your head. I bought a book "how to calculate quickly" to help me with that. MOst

I would start with number theory and getting very good at managing numbers in your head. I bought a book "how to calculate quickly" to help me with that. MOst algebra and calculus problems could be solved quite easily by running approximations in your head that solve the equation at hand. I learned this method from prof Feynman in his famous book "you must be joking Mr Feynman"