Ratios, Fractions & Percentages

What are ratios and fractions and why do they matter?

A ratio is a comparison of two numbers. We generally separate the two numbers in the ratio with a colon (:).  Suppose we want to write the ratio of 8 and 12.  We can write this as 8:12 or as a fraction 8/12.  A proportion is an equation with a ratio on each side. It means that two ratios are equal.  And a percentage is a way of expressing a number as a fraction of 100 (per cent meaning "per hundred").  It is often denoted using the percent sign, "%", or the abbreviation "pct". For example, 45% (read as "forty-five percent") is equal to 45 / 100, or 0.45. 

Why do they matter? Ratios, fractions and percents are used everywhere in life!  For example, they are used to figure out how many eggs to cups flour are needed when you bake a cake or how many miles per gallon a car consumes.  And video and computer game designers use ratios and proportions to design the graphics in their games.

View this video about Ratios, Proportions, Units, and Rates


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NSF logo This material is based upon work supported by the National Science Foundation under Grant No. DUE-0840824. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.