You need to know the least common denominator (LCD) of 5 and 21 if you want to add or subtract two fractions with 5 and 21 as denominators.
The least common denominator, also called lowest common denominator (LCD), of 5 and 21 is 105.
Here is a math problem example where you need to know the LCD of 5 and 21 to solve:
3/5 + 2/21 = ?
Step 1) Take the LCD and divide each denominator by it as follows:
105/5 = 21
105/21 = 5
Step 2) Multiply each nominator with the respective answers from Step 1:
3 x 21 = 63
2 x 5 = 10
Step 3) Put it all together to solve the problem:
63/105 + 10/105 = 73/105
= 3/5 + 2/21 = 73/105
It's that easy! Once again, the lowest common denominator (LCD) of 5 and 21 is as follows:
105
Find Least Common Denominators
Enter another two numbers below to find the Least Common Denominator.