Remember to go get the TI-36a scientific calculator!
Knowing your divisibility rules will be a great help to you through your math career. It makes simplifying and factoring even easier because there isn't as much guess work. Take a look at the video and practice the rules as much as you can to make sure they stay fresh.
Read the rules and see examples
Mathsisfun.com - Divisibility Rules
Watch the video here
Math Playground Divisibility Rules
Practice