Different ratios can represent the same amount. When two ratios are set equal to each other, they form a proportion. Each ratio is given in its fractional form, with the numbers being compared set up as a numerator and a denominator. Though the two ratios might appear completely unrelated, the relationship that each ratio's numerator has with its denominator can make the fractions equivalent and the ratios equal. The process of cross-multiplication works with the ratios' numerators and denominators in determining whether the proportion is true or false.
Instructions
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1
Obtain two ratios for comparison. In this example, let the proportion be 5/7 = 35/49.
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2
Multiply the first ratio's numerator to second ratio's denominator. In this example, multiplying 5 by 49 equals 245.
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3
Multiply the second ratio's numerator by the first ratio's denominator. In this example, multiplying 7 by 35 equals 245.
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Compare the two products. If they are equal, the proportion is true, and if they are not equal, the proportion is false. Concluding this example, both products are 245 and therefore equal, so the proportion is true.