Least Common Denominator (LCD) of 3, 9, and 21

The Least Common Denominator of 3, 9 and 21, also known as the Lowest Common Denominator of 3, 9 and 21, is useful if you need to add, subtract, or compare three fractions with the denominators of 3, 9 and 21.

The fractions with 3, 9 and 21 denominators will look like this:

 X 3

 Y 9

 Z 21

The Least Common Denominator of 3, 9 and 21 is 63.

You need to multiply 3 by 21, 9 by 7, and 21 by 3 to make them all 63. Furthermore, you need to multiply the numerators by the same amounts to keep the fraction values the same.

Therefore, you have to make the following calculations so the fractions keep the same value and get the same denominator:

 X x 21 3 x 21

 Y x 7 9 x 7

 Z x 3 21 x 3

Which gives you the following three new fractions that you can add, subtract and compare:

 21X 63

 7Y 63

 3Z 63

You can substitute X, Y and Z with the numerators of your fractions with 3, 9 and 21 denominators. This way you can add, subtract and compare your fractions correctly.

Least Common Denominator Calculator
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Least Common Denominator (LCD) of 3, 9 and 22
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Notes

The Least Common Denominator of 3, 9 and 21 is the same as the Least Common Multiple of 3, 9 and 21.

To calculate what to multiply each denominator and corresponding numerator by, we divided the LCD by each of the denominators.

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