When and why should you find the LCM?

Answer 1

The LCM (least common multiple) is the smallest positive whole number exactly divisible by two or more given whole numbers. Example: the LCM of 14 and 35 is 70 because 70/14=5 and 70/35=2, and no number smaller than 70 is exactly divisable by 14 and 35.

The LCM can also found be for more complex numbers by taking the multiple of the highest power of prime factors from both numbers. For example, the LCM of 72 and 90 is 360, which is the multiple of the highest power of prime factors from both numbers (23 x 32 x 5 = 2 x 2 x 2 x 3 x 3 x 5 = 360). (Prime factors: 72 = 23 x 32; 90 = 2 x 32 x 5)

For more than two numbers, LCM can be found by taking the multiple of the highest power of prime factors from all numbers. For example, the LCM of 28, 70, and 98 is 4,900, which is the multiple of the highest power of prime factors from all three numbers (22 x 52 x 72 = 2 x 2 x 5 x 5 x 7 x 7 = 4900). (Factors: 28 = 22 x 7; 98 = 2 x 72; 350 = 2 x 52 x 7)

Answer 2

When you want to add or subtract fractions and need to find a common denominator.

Answer 3

When you are trying to add or subtract unlike fractions.

Answer 4

I'm a carpenter. I have to add unlike fractions (1/4, 3/8, 5/16) every day. To do that, I have to find the lowest common denominator, which is the same process as the LCM.

Answer 5

You will need to find the LCM in order to add and subtract fractions.

Answer 6

When you are adding and subtracting fractions.

Answer 7

It is useful to find the LCM when you want to add and subtract fractions. It is useful to find the GCF when you want to reduce fractions.

Answer 8

Finding the LCM helps in the process of adding and subtracting unlike fractions.

Answer 9

Most often in comparing, adding and subtracting fractions.