A ratio is a comparison of two numbers. Ratios can be expressed as a fraction, such as 4/7, or as two numbers with a colon, such as 4:7. You would say the ratio is four to seven. Ratios are common in business, finance, science and technology. Understanding ratios is also useful in everyday life. Examples of common ratios include miles per gallon and dollars per pound. It is difficult to mentally compute how a fraction such as 4/7 compares to 13/21. By converting the ratios to decimal numbers or percentages, you can compare them on a level field.

Divide the numerator by the denominator of one ratio. For example, if the ratio is 4/7, then divide 4 by 7. This will yield a decimal number between zero and one. Round to the second decimal point. In this example, 4/7 equals 0.57.

Divide the numerator by the denominator of the other ratio. For example, if the second ratio is 9/15, divide 9 by 15. Round to the second decimal point. In this example, 9/15 equals .60.

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Compare the two numbers. The ratios are now being expressed on equal terms. Convert the ratios to percentage numbers by multiplying the decimal number by 100. In the first example, 4/7 became .57, which equals 57%. In the second ratio, 9/15 became .60, which equals 60%. Therefore, 4/7 (57%) is less than 9/15 (60%).