You need to know the least common denominator (LCD) of 5 and 15 if you want to add or subtract two fractions with 5 and 15 as denominators.
The least common denominator, also called lowest common denominator (LCD), of 5 and 15 is 15.
Here is a math problem example where you need to know the LCD of 5 and 15 to solve:
3/5 + 2/15 = ?
Step 1) Take the LCD and divide each denominator by it as follows:
15/5 = 3
15/15 = 1
Step 2) Multiply each nominator with the respective answers from Step 1:
3 x 3 = 9
2 x 1 = 2
Step 3) Put it all together to solve the problem:
9/15 + 2/15 = 11/15
= 3/5 + 2/15 = 11/15
It's that easy! Once again, the lowest common denominator (LCD) of 5 and 15 is as follows:
15
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