Step 1 : Place the numbers inside division bar:

Step 2 : Find a prime number which divides both numbers.

In this example we can divide by 2. If any number is not divisible by 2 write it down unchanged.

Step 3 : Repeat Step 2 until you can no longer divide.

Since there are no primes that divides at least two of given numbers, we conclude that the LCM is a product of starting numbers.

LCM = 12 · 140 = 420

This solution can be visualized using a Venn diagram.

The LCM is equal to the product of all the numbers on the diagram.