If you have a hard time spending your free time why don’t you try doing a bit of Sudoku? Sudoku is very entertaining and is good for your brain, it works on mathematical calculations and will certainly strengthen your mathematical calculations area of your brain.
I play Sudoku many times and if you haven’t tried maybe you should take a look, Getting to Grips with Sudoku is a site that will expand your Sudoku horizons.
This game popularized by the Japanese has become known all over the world and there is a reason for it.
You can find Sudoku books through Amazon.com and www.macadamiapublishingllc.com.