How is the least common multiple used when adding and subtracting fractions?

Answer 1

One way to compare fractions is with common denominators. The process is the same as finding the LCM of integers.

Example: 1/30 and 1/42

Factor them.

2 x 3 x 5 = 30

2 x 3 x 7 = 42

Combine the factors, eliminating duplicates.

2 x 3 x 5 x 7 = 210

1/30 = 7/210

1/42 = 5/210

1/30 > 1/42

Answer 2

Example: 1/30 and 1/42
The LCM (LCD) of 30 and 42 is 210.
30 x 7 = 210, so multiply the fraction by 7/7.
1/30 = 7/210
42 x 5 = 210, so multiply the fraction by 5/5
1/45 = 5/210

Answer 3

After finding the LCM use it as the denominator.

Multiply by what would change the denominator to the LCM.

Like 1/4 and 1/18

The least common multiple of 4 and 18 is 36.

4x9=36

18x2=36

Answer 4

Example: 2/3 and 3/4

To find the least common denominator it is necessary to find the least common multiple of 3 and 4, which is 12.

2/3 = 8/12

3/4 = 9/12

2/3 + 3/4 = 17/12 = 1 and 5/12

Answer 5

When adding and subtracting unlike fractions, find the LCM of the denominators and convert them to it. In this case, it's called the least common denominator, but it's the same process.