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Compare ratios using equivalent forms

The comparison of two ratios involves rewriting them in equivalent forms by multiplying or dividing both terms by the same nonzero factor, such as expressing them as fractions with a common denominator or as unit rates with a common first quantity. This preserves each multiplicative relationship and allows the ratios to be ordered or identified as equal; comparing corresponding terms independently can give an incorrect conclusion. The reasoning supports proportional relationships, percent, rate, and scale-factor problems.

Detailed Explanation: Compare ratios using equivalent forms

To compare two ratios, rewrite them in an equivalent form that makes the comparison easy. You may multiply or divide both terms of a ratio by the same nonzero number. This keeps the ratio’s value unchanged.

Example: Which is greater, 3:53:5 or 4:74:7?

Rewrite each ratio as a fraction:

3:5=35and4:7=473:5=\frac{3}{5} \qquad\text{and}\qquad 4:7=\frac{4}{7}

Find a common denominator. Both 55 and 77 divide into 3535.

  • Multiply 35\frac{3}{5} by 77\frac{7}{7}:
35=3757=2135\frac{3}{5}=\frac{3\cdot7}{5\cdot7}=\frac{21}{35}
  • Multiply 47\frac{4}{7} by 55\frac{5}{5}:
47=4575=2035\frac{4}{7}=\frac{4\cdot5}{7\cdot5}=\frac{20}{35}

Now compare the numerators:

2135>2035\frac{21}{35}>\frac{20}{35}

Therefore,

3:5>4:7\boxed{3:5>4:7}

Remember to multiply or divide both parts of each ratio by the same number. Comparing the terms separately—for example, saying 4:74:7 is greater because 4>34>3—can lead to an incorrect conclusion.

Learn by doing: Compare ratios using equivalent forms

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Fraction Comparison - Basic - One Changed Denominator


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