Aximili85 wrote:

Karishma sorry for such a basic question, but how do you calculate the LCM between different numbers, im forgetting my basics here..

LCM is the lowest common multiple. To get the LCM of some numbers, you split the number into its prime factors.

\(12 = 2^2 * 3\)

\(18 = 2*3^2\)

\(24 = 2^3*3\)

Now LCM is the number that includes all the factors of each of these numbers.

\(LCM = 2^3 * 3^2 = 72\)

We take 2^3 because the highest power of 2 in any number is 2^3 so we need at least three 2s in the LCM.

We take 3^2 because the highest power of 3 in any number is 3^2 so we need at least two 3s in the LCM.

Instead, if the numbers are:

\(12 = 2^2 * 3\)

\(14 = 2*7\)

\(LCM = 2^2*3*7\)

When looking for LCM of 12, 14, 18, 21, we know that the LCM must have each of these numbers as the factor.

So I took 12 since the first number is 12.

14 has 2 which is already included in 12 and it has 7 which is not included in 12 so we need to take a 7 too. We get 12*7

18 has a 2 which is already included in 12 and it has two 3s but 12 has only one 3. So we need another 3. We get 12*7*3

21 has 3 and 7 and they both are already included.

LCM = 12*7*3

_________________

Karishma

Veritas Prep | GMAT Instructor

My Blog

Get started with Veritas Prep GMAT On Demand for $199

Veritas Prep Reviews