You need to know the least common denominator (LCD) of 6 and 21 if you want to add or subtract two fractions with 6 and 21 as denominators.
The least common denominator, also called lowest common denominator (LCD), of 6 and 21 is 42.
Here is a math problem example where you need to know the LCD of 6 and 21 to solve:
3/6 + 2/21 = ?
Step 1) Take the LCD and divide each denominator by it as follows:
42/6 = 7
42/21 = 2
Step 2) Multiply each nominator with the respective answers from Step 1:
3 x 7 = 21
2 x 2 = 4
Step 3) Put it all together to solve the problem:
21/42 + 4/42 = 25/42
= 3/6 + 2/21 = 25/42
It's that easy! Once again, the lowest common denominator (LCD) of 6 and 21 is as follows:
42
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