Editing Ratio (section)

==Proportions and percentage ratios{{anchor|Proportions|Percentage ratios}}==
If we multiply all quantities involved in a ratio by the same number, the ratio remains valid. For example, a ratio of 3:2 is the same as 12:8. It is usual either to reduce terms to the [[lowest common denominator]], or to express them in parts per hundred ([[percent]]).

If a mixture contains substances ''A'', ''B'', ''C'' and ''D'' in the ratio 5:9:4:2, then there are 5 parts of ''A'' for every ''9'' parts of ''B'', 4 parts of ''C'', and 2 parts of ''D''. As {{nobr|5 + 9 + 4 + 2 {{=}} 20,}} the total mixture contains 5/20 of ''A'' (5 parts out of 20), 9/20 of ''B'', 4/20 of ''C'', and 2/20 of ''D''. If we divide all numbers by the total and multiply by 100, we have converted to [[percentages]]: 25% ''A'', 45% ''B'', 20% ''C'', and 10% ''D'' (equivalent to writing the ratio as 25:45:20:10).

If the two or more ratio quantities encompass all of the quantities in a particular situation, it is said that "the whole" contains the sum of the parts: for example, a fruit basket containing two apples and three oranges and no other fruit is made up of two parts apples and three parts oranges. In this case, <math>\tfrac{2}{5}</math>, or 40% of the whole is apples and <math>\tfrac{3}{5}</math>, or 60% of the whole is oranges. This comparison of a specific quantity to "the whole" is called a proportion.

If the ratio consists of only two values, it can be represented as a fraction, in particular as a decimal fraction. For example, older [[television]]s have a 4:3 ''[[Display aspect ratio|aspect ratio]]'', which means that the width is 4/3 of the height (this can also be expressed as 1.33:1 or just 1.33 rounded to two decimal places). More recent widescreen TVs have a 16:9 aspect ratio, or 1.78 rounded to two decimal places. One of the popular widescreen movie formats is 2.35:1 or simply 2.35. Representing ratios as decimal fractions simplifies their comparison. When comparing 1.33, 1.78 and 2.35, it is obvious which format offers wider image. Such a comparison works only when values being compared are consistent, like always expressing width in relation to height.