You need to know the least common denominator (LCD) of 21 and 5 if you want to add or subtract two fractions with 21 and 5 as denominators.
The least common denominator, also called lowest common denominator (LCD), of 21 and 5 is 105.
Here is a math problem example where you need to know the LCD of 21 and 5 to solve:
3/21 + 2/5 = ?
Step 1) Take the LCD and divide each denominator by it as follows:
105/21 = 5
105/5 = 21
Step 2) Multiply each nominator with the respective answers from Step 1:
3 x 5 = 15
2 x 21 = 42
Step 3) Put it all together to solve the problem:
15/105 + 42/105 = 57/105
= 3/21 + 2/5 = 57/105
It's that easy! Once again, the lowest common denominator (LCD) of 21 and 5 is as follows:
105
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