Let a and b are two numbers, then

a * b = LCM(a, b) * HCF(a, b)

Let us take some examples regarding your question

Ex 1: Three numbers are in the ratio 1 : 2 : 3 and their HCF is 12. What are these numbers?

Solu: Let the numbers are x, 2x, 3x

Now given HCF(x, 2x, 3x) = 12

=> x = 12                          

So, the numbers are 12, 2*12, 3*12 = 12, 24, 36

Ex 2: Two numbers are in the ratio 3 : 4 and their HCF is 4. What is their  LCM?

Solu: Let the numbers are 3x, 4x

Now given HCF(3x, 4x) = 4

=> x = 4                         

So, the numbers are 3*4, 4*4 = 12, 16

Now, LCM(12, 16) = 48

Hope you got the point.