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:



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:



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



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
Please enter another two or three denominators below so we can calculate the Least Common Denominator (LCD) for you:
Least Common Denominator (LCD) of 3, 9 and 22
Here is the next set of numbers we have calculated the LCD for.
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.