Lemon Image If limes are priced at 3 for $1, then you can buy 6 for $2, 9 for $3, and so on. In mathematical terms,

3 : $1 = 6 : $2 = 9 : $3

Here, we are using a concept called proportion, whether we realize it or not.

Proportions

A proportion is an equation stating that two ratios are equal. Proportions are usually written in one of these two ways:

a : b = c : d
or
a / b = c / d

in which a, b, c, and d are real numbers and b Not Equal Symbol 0 and d Not Equal Symbol 0.

In either of the above two forms, the terms b and c are called the means of the proportion and the terms a and d are called the extremes. The multiplication property of equality shows that in any proportion the product of the means is equal to the product of the extremes: ad = bc.

If only one term of the proportion is a variable, then its value can be found by solving the proportion.

  [Experiment] [Exercise]