Which positive integers less than 12 are relatively prime to 12?

2 numbers are relatively prime, if they have no common factor except 1.

The positive integers less than 12 are {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}

12 and  {2, 4, 6, 8, 10} have 2 as a common factor

12 and {3, 9} have 3 as a common factor.

{1, 5, 7, 7} are left. These numbers have no common factor with 12 except 1.

{1, 5, 7, 11}