7.RP.2c: Equating Proportional Relationships: An Example with Cost and Quantity

Grade: 7th Grade

Domain: RP: Ratios and Proportional Relationships

Standard Description

Represent proportional relationships by equations. For example, if total cost t is proportional to the number n of items purchased at a constant price p, the relationship between the total cost and the number of items can be expressed as t = pn.

Domain Description

Compute the rates associated with ratios of fractions, like lengths and areas. For instance, for a person walking 1/2 mile every 1/4 hour, the rate would be denoted as 1/2/1/4 miles per hour, or 2 miles per hour.

Determine if two quantities share a proportional relationship by observing if the graph of their ratios is a straight line through the origin. Recognize the constant of proportionality in different formats such as tables, diagrams, and verbal descriptions.

Create equations to represent proportional relationships. As an example; if the total cost is proportional to the number of items bought at a rate p, the equation becomes t = pn.

Interpret what a point (x, y) on a graph of a proportional relationship means considering points like (0, 0) and (1, r), where r represents the unit rate.

Employ proportional relationships to tackle multistep ratio and percent calculations, such as simple interest, taxes, markups and markdowns, commissions, fees, and percent variations.