What is a Proportion? Definition and Examples

What is a proportion? The statement that two ratios are equal is called a proportion. For example, 2 / 5 is a ratio and 4 / 10 is also a ratio.

Notice that 2 / 5 = 0.4 and 4 / 10 = 0.4 

Since 2 / 5 and 4 / 10 are equal to the same number or decimal, we call the equation 2 / 5 = 4 / 10 a proportion.

More examples of proportions

1 / 2 = 5 / 10

1 / 3 = 2 / 6

5 / 7 = 15 / 21

3 / 4 = 6 / 8

1 / 9 = 3 / 27

5 / 2 = 15 / 6

What is a proportion in real life?

A classroom has 6 males and 9 females while a movie theater has 100 males and 150 females. Does this situation form a proportion?  

The ratio of males to females in the classroom 6 / 9 = 0.666666

The ratio of males to females in the movie theater 100 / 150 = 0.666666

Therefore, 6 / 9 = 100 / 150 is a proportion since both 6 / 9 and 100 / 150 are equal to the same number or 0.666666.