Question

what is the lmc of two numbers that have no common factors greater then 1

Answer 1

We can take prime numbers so they don't have a common factor other than 1.

3, and 5.

So we have to list the multiples to find the LCM

3: 3, 6, 9, 12, 15, 18
5: 5, 10, 15, 20, 25

15 is the LCM of 3 and 5

So, you can notice that if two numbers, lets call them a and b, have no common factor, then $a \times b$ is the LCM.

Hope that helped :)