What is the fastest and easiest way to find the LCM?

Answer 1

• Find the prime factorisation of each of the two numbers.
• Select the primes which appear in both factorisations.
• Multiply these factors together.

The answer is the GCF.

If a prime factor appears n times in each factorisation then it must appear n times in the list of factors to be multiplied together.

Answer 2

Prime factorization.

Example: 30 and 42

Factor them.

2 x 3 x 5 = 30

2 x 3 x 7 = 42

Select the common factors.

2 x 3 = 6, the GCF.

Answer 3

You need at least two numbers to find a GCF. Once you have them, you can

1. Compare their lists of factors, or

2. Compare their prime factorizations.

Answer 4

Example: 30 and 42
Factor them.
2 x 3 x 5 = 30
2 x 3 x 7 = 42
Select the highest amount of each factor.
2 x 3 x 5 x 7 = 210, the LCM

Answer 5

Example: 30 and 42

Factor them.

2 x 3 x 5 = 30

2 x 3 x 7 = 42

Select the common factors.

2 x 3 = 6, the GCF

Answer 6

Example: 30 and 42

Factor them.

2 x 3 x 5 = 30

2 x 3 x 7 = 42

Select the common factors.

2 x 3 = 6, the GCF

Answer 7

Dividing them by prime numbers