Three numbers are in ratio 1 : 2 : 3 and HCF is 12. The numbers are:

Since, the numbers are given in the form of ratio that means their common factors have been cancelled.
Each one's common factor is HCF.
And here HCF = 12,
hence, the numbers are 12, 24 and 36.

Alternatively, Let the numbers be x, 2x and 3x.
The HCF in x, 2x and 3x is x because 1, 2, 3 are prime.
Hence,
x = 12; then the other numbers are 24 and 36.