Ratios and proportions

When we talk about the speed of a car or an airplane we measure it in miles per hour. This is called a rate and is a type of ratio. A ratio is a way to compare two quantities by using division as in miles per hour where we compare miles and hours.

A ratio can be written in three different ways and all are read as “the ratio of x to y”

X to Y

X : Y

X / Y

A proportion on the other hand is an equation that says that two ratios are equivalent. For instance, if one package of cookie mix results in 20 cookies than that would be the same as to say that two packages will result in 40 cookies.

20/1 = 40 2

A proportion is read as “x is to y as z is to w”

X / y= z / w

Where y, w≠0

If one number in a proportion is unknown you can find that number by solving the proportion.