You need to know the least common denominator (LCD) of 21 and 8 if you want to add or subtract two fractions with 21 and 8 as denominators.
The least common denominator, also called lowest common denominator (LCD), of 21 and 8 is 168.
Here is a math problem example where you need to know the LCD of 21 and 8 to solve:
3/21 + 2/8 = ?
Step 1) Take the LCD and divide each denominator by it as follows:
168/21 = 8
168/8 = 21
Step 2) Multiply each nominator with the respective answers from Step 1:
3 x 8 = 24
2 x 21 = 42
Step 3) Put it all together to solve the problem:
24/168 + 42/168 = 66/168
= 3/21 + 2/8 = 66/168
It's that easy! Once again, the lowest common denominator (LCD) of 21 and 8 is as follows:
168
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