Here is a mixing container that does the math for you.Just fill the container with oil to the appropriate amount of fuel added at the appropriate mixing rate. Easy as pie.Google SeaSence oil mixing bottle or google search this link.I use this personally,hope it helps

http ://www.amazon.com/SeaSense-MIXING-BOTTLE-50091443-Reference/dp/B000W6QJIO

First post for me but long time reader.
Boat/fishing Bio..
1998 Ranger692
175hp Evinrude intruder
walleye fishing seriously bass fisherman for fun