how to do a percentage
1. Know what a percentage is. A percentage is a way to express a number as a part of a whole. To calculate a percentage, we look at the whole as equal to 100%.For example, say you have 10 apples (=100%). If you eat 2 apples, then you have eaten 2/10 Ã 100% = 20% of your apples and you are left with 80% of your original apples.. Know what a percentage is. A percentage is a way to express a number as a part of a whole. To calculate a percentage, we look at the whole as equal to 100%.