You need to know the least common denominator (LCD) of 5 and 7 if you want to add or subtract two fractions with 5 and 7 as denominators.
The least common denominator, also called lowest common denominator (LCD), of 5 and 7 is 35.
Here is a math problem example where you need to know the LCD of 5 and 7 to solve:
3/5 + 2/7 = ?
Step 1) Take the LCD and divide each denominator by it as follows:
35/5 = 7
35/7 = 5
Step 2) Multiply each nominator with the respective answers from Step 1:
3 x 7 = 21
2 x 5 = 10
Step 3) Put it all together to solve the problem:
21/35 + 10/35 = 31/35
= 3/5 + 2/7 = 31/35
It's that easy! Once again, the lowest common denominator (LCD) of 5 and 7 is as follows:
35
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