You need to know the least common denominator (LCD) of 21 and 79 if you want to add or subtract two fractions with 21 and 79 as denominators.
The least common denominator, also called lowest common denominator (LCD), of 21 and 79 is 1659.
Here is a math problem example where you need to know the LCD of 21 and 79 to solve:
3/21 + 2/79 = ?
Step 1) Take the LCD and divide each denominator by it as follows:
1659/21 = 79
1659/79 = 21
Step 2) Multiply each nominator with the respective answers from Step 1:
3 x 79 = 237
2 x 21 = 42
Step 3) Put it all together to solve the problem:
237/1659 + 42/1659 = 279/1659
= 3/21 + 2/79 = 279/1659
It's that easy! Once again, the lowest common denominator (LCD) of 21 and 79 is as follows:
1659
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