How to Cross Multiply Proportions
A proportion is the name given to two ratios or fractions that are equal. Proportions can be written two ways: b/c=d/e or b:c=d:e. Proportions are solved by cross multiplying.
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Instructions
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How to Cross Multiply Proportions
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1
Multiply the numerator on the left side by the denominator on the right side.For example: in 16/32=1/2, we would multiply 16 (the numerator on the left side) by 2 (the denominator on the right side).
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2
Write the product from step one. Continuing with the same example, we would write 32 ( the product from step one).
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3
Write an equal sign after the product from step one. Continuing with our example, we would already have 32. We would then add an equal sign: 32=.
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4
Multiply the denominator on the left side by the numerator on right side. Continuing with the same example, 16/32=1/2, we would multiply 32 (the denominator on the left side) by 1 (the numerator on the right side).
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5
Write the product from step four on the right side (32) of the equal sign. Remember that we had 32= from step three. Now we will add the product from step four on the right side of this: 32=32. If both numbers are the same, it is a proportion.
How to Cross Multiply Proportions With a Variable or Missing Number
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6
Do steps one through five in section one.
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7
Divide both sides by the coefficient. For example, in 3x., 3 is the coefficient.
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8
Write the variable (the letter that stands for the number) on the left side.
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9
Write an equal sign to the right side of the variable.
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10
Write the answer on the side without the variable.
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