A proportion is a statement of equality between two ratios.

2:3:8 = 4:6:16

Proportions are used to solve problems involving ratios.

Problem: Since 100 cm is equivalent to 1 m, how many metres are equivalent to 57.3 cm?

Notice that whether centimetres or metres is in the numerator of each ratio of the proportion, the result is the same (0.573 m are equivalent to 57.3 cm).

Notice that whether the unknown is in the numerator or the denominator of a ratio of the proportion, the result is the same (0.573 m are equivalent to 57.3 cm).