Percentages are defined as a fraction or portion of a whole. Generally percentages deal with an amount out of one hundred but can be used in sales, economics, and science. If you've walked into any store you're sure to find something marked a certain percent off. Fractions are not whole numbers with a numerator over a denominator. Usually the numerator and denominator are expressed as integers. There are four types of fractions: simple fractions, complex fractions, mixed fractions, and improper fractions. Decimals are also not integers. They are expressed often like 0.34 and are often rounded off since some go for too long. Both decimals and fractions are also used to convert to percentages.