You need to know the least common denominator (LCD) of 3 and 18 if you want to add or subtract two fractions with 3 and 18 as denominators.
The least common denominator, also called lowest common denominator (LCD), of 3 and 18 is 18.
Here is a math problem example where you need to know the LCD of 3 and 18 to solve:
3/3 + 2/18 = ?
Step 1) Take the LCD and divide each denominator by it as follows:
18/3 = 6
18/18 = 1
Step 2) Multiply each nominator with the respective answers from Step 1:
3 x 6 = 18
2 x 1 = 2
Step 3) Put it all together to solve the problem:
18/18 + 2/18 = 20/18
= 3/3 + 2/18 = 20/18
It's that easy! Once again, the lowest common denominator (LCD) of 3 and 18 is as follows:
18
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