You can brush up your Maths by practicing mental arithmetic - something which has been lacking in UK schools since I were a lad so not sure if this is something you get taught much in Scandanavia.
There are plenty of websites out there with mental maths problems of a practical nature which will also help you with your flying to some degree (i.e., burning fuel at 14 gals per hour with 40 gals, what is your endurance)