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what is proportion

A proportion is a name we give to a statement that two ratios are equal. It can be written in two ways:

• two equal fractions, a/b = c/d

or,

• using a colon,    a:b = c:d

When two ratios are equal, then the cross products of the ratios are equal.

That is, for the proportion, a:b = c:d ,  a x d = b x c