Let n be a positive integer greater than or equal to 3. Let a,b be integers such that ab is invertible modulo n and \((ab)^{-1}\equiv 2\pmod n\). Given a+b is invertible, what is the remainder when \((a+b)^{-1}(a^{-1}+b^{-1})\) is divided by n?
I don't understand how this problem works/what it's asking. An explanation woud help, because I don't know how to solve this either!
