The Sims Online:
Logic

Logic is a fun skill to learn - you can become more logical by playing chess alone or with friends! Many houses have a whole group of chess-players enjoying themselves.

You can then use the logic in the treasure hunt game, or the code-breaking game. Those are both good ways to make money. There are also chalkboards where you can work alone on solving equations, and sell the solutions for around $50-$100 every 5 minutes or so.

The Sims Online Tips, Techniques and Walkthroughs