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Concept

$ba =dc ora:b=c:d $

The first and last numbers in the proportion are called the extremes, while the other two numbers are called the means.
$ad↓means:↑b =↑c : extremes d↓ $

In a proportion, by the Cross Products Property, the product of the $extremes$ is equal to the product of the $means.$

If $ba =dc ,$ then $ad=bc.$

In this case, one-third of a pizza is the same amount of pizza as two-sixths or four-twelfths. If the simplified forms of two fractions are equal, then they are said to be proportional. For example, one-third is proportional to two-sixths and four-twelfths.

Note that proportions are often used in geometric concepts such as the Triangle Proportionality Theorem or when determining if two figures are similar.

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