I'm actually studying for the ASVAB right now, and this is one of the things I have to know for this test. So, I remember back to my high school days where my science teacher taught us about this pyramid, which will help you to visualize how to get Watts, Voltage, or Amperage in a situation where you have at least two of the numbers.

I whipped this up in Photoshop real quick - hopefully you'll find it useful



How it works:

If you have two numbers, then you cover up the letter that you need. In this case, you need to know Wattage. So you take your hand/finger and cover up the "W" and that leaves you with "A" (Amps) and "V" (Voltage). Since they are side by side, that indicates that you multiply those numbers to get wattage.

Lets say you need to know Amps - You would then cover up the "A", and then notice how the "W" is on top of the "V" - this indicates that you would divide W over V

It would work the same way if you needed to know Voltage - Cover up the "V", and then notice how the W is over the A, indicating that you would divide W/A

Hope this helps