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Proportional Webs

Proportional Webs

Author: Rebecca Newburn

Many relationships are proportional. Learn how to identify them.

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Questions to think about:

  • What is a proportional relationship?
  • How can I tell if the relationship is proportional?

Proportional Relationships

A proportional relationship is when the growth pattern is multiplied by a scale factor.

We'll be exploring how a relationship can be expressed in a situation. For example, Malia buys bird 1 lb. of bird seed for $3. If she buys 2 lbs., she would spend $6. Since she is charged the same amount per pound, and there is no initial fee, this is a proportional relationship.

Malia's Birdseed

Lbs 1 2 3 4
Cost ($) 3 6 9 12

You can write each point as a fraction in simplest terms and if they are all equal, then it's a proportion. Ex. 1 third equals 2 over 6 equals 3 over 9 equals 4 over 12 because they all simplify to 1 third.

You can tell if a graph is proportional because it is 1) linear (a line) and 2) goes through the origin (0, 0).

The relationship between the quantities can be written in the form of y = kx. k is the constant of proportionality. The constant of proportionality is the same as the scale factor.

Proportional or Not Proportional?

For equations, the equation is in the form of y = kx. k is the constant of proportionality. The instructor mentioned that if it is a one-step equation it's proportional. NOTE: y = x + k, which is a one-step equation, is NOT proportional. Only one step equations in the form y = kx are proportional.

Source: Danielle Kunetz

Source: Ms. Newburn