Question

What is the HCF / GCF of 120, 180 and 190
in prime factorisation method

Answer 1

120 = 10 x 3 x 2 x 2
180 = 10 x 3 x 3 x 2
190 = 10 x 19

the HCF (highest common factor) is 10

I don't know what you mean by GCF,
to me it would mean "greatest common factor" which is the same as the HCF
Did you mean GCM, (greatest common multiple ?)
then it would be
10x3x3x2x2x19 or 6840

so for HCF/GCM = 10/6840 = 1/684
- I don't see why you would ever need that fraction.

Answer 2

actually, 6840 is the Least common multiple. There is no greatest multiple.