In mathematics, a percentage's a way of expressing a number as a fraction of 100 (per cent meaning "per hundred"). It's often denoted using the percent sign, "%". For example, 45% (read as "forty-five percent")'s equal to 45 / 100, or 0.45. Percentages are used to express how large one quantity's, relative to another quantity. The first quantity usually represents a part of, or a change in, the second quantity, which should be greater than zero. For example, an increase of $ 0.15 on a price of… (More on Percentage)