Grade 7 · Number · Proportional Relationships
Test a Proportional Relationship
Two quantities are proportional when they change at a constant multiplicative rate and the relationship begins at the origin.
The big idea
A proportional relationship has one constant of proportionality
If every notebook costs $3, cost = 3 × number of notebooks. The ratio cost/notebooks remains 3 and the graph passes through (0, 0).
Work it through
Find the cost of 14 notebooks
- 1. Write two equivalent ratios: $3/1 notebook = x/14 notebooks.
- 2. Scale 1 notebook to 14 by multiplying by 14.
- 3. Scale the cost by the same factor: 3 × 14 = 42.
- 4. The cost is $42; verify that 42 ÷ 14 = 3.