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Grade 8 · Number · Proportional Reasoning

Compare Proportional Situations

Equivalent ratios describe the same multiplicative relationship. Tables, graphs, equations, and scale factors reveal that relationship in different ways.

The big idea

A proportion preserves one multiplicative relationship

If 6 items cost $9, the unit rate is $1.50 per item. Scaling both quantities by the same factor creates an equivalent situation.

Work it through

Find the cost of 14 items at 6 for $9

  1. 1. Find the unit rate: 9 ÷ 6 = 1.5 dollars per item.
  2. 2. Multiply by the requested quantity: 14 × 1.5 = 21.
  3. 3. The cost is $21.
  4. 4. Verify that 21/14 = 9/6 = 1.5.