Which Marble is the heaviest ?

There are 8 marbles that weigh 1 ounce each, and 1 marble that weighs 1.1 ounces.
The marbles are all uniform in size, appearance, and shape.
You have a balance that contains 2 trays.
You are only able to use the scale 2 times.
How do you determine which marble is the heaviest
using only the scale and marbles in 2 weighings.
Answers :
Place 3 marbles on each tray.
- If the first weighing doesn't balance, remove all the marbles from the lighter side, and place one marble on each tray from the heavier tray. The heavier side is the 1.1 ounce marble, but if they balance, then the marble from the heavier tray from the first weighing that was not weighed in the second weighing is the heavier one(1.1).
- If the marbles balance on the first wieiging, remove the marbles from the trays, and place 2 of the remaining unweighed marbles on the trays, one on each tray. If one is heavier, it is the heavier marble(1.1), but if they balance, the remaining unweighed marble is the heavier one.