Big Ideas Math: Modeling Real Life, Grade 7
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Big Ideas Math: Modeling Real Life, Grade 7 View details
4. Writing and Solving Proportions
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Exercise 1 Page 208

Two quantities are proportional if there is a constant unit rate, or ratio, each time the values change.

Not proportional

Practice makes perfect
Two quantities are proportional if there is a constant unit rate or ratio each time the values change. To determine if x and y are proportional, let's find the ratios yx for each pair of x and y. If all ratios are the same, x is proportional to y.
x y y/x Value
4 6 6/4 1.5
6 8 8/6 1 13
8 10 10/8 1.25

Notice that value of yx differs from pair to pair. This means x is not proportional to y.