Defining The Constant Of Proportionality

Proportional Relationships

Formative Assessment

Summary of the Math: Proportional Relationships

Read and Discuss

The relationship between two varying quantities can be expressed by a constant ratio. For example, the ratio of tricycle wheels to tricycles is 3 : 1.

You can write: wt=31

This relationship is an example of a proportional relationship, because even if the total number of tricycle wheels or the total number of tricycles varies, the ratio between the tricycle wheels and the tricycles will remain the same. You say: “The number of wheels is proportional to the number of tricycles.”

You can write: w = 3t

You can also express this relationship as the ratio of tricycles to wheels: the ratio is 1 to 3, or 1 : 3. You say: “The number of tricycles is proportional to the number of wheels.”

You can write: tw=13 or t=13w


Can you:

  • Write a formula using the constant of proportionality?
  • Calculate the constant of proportionality from a table of values?