You need to find a common denominator. I would use 6 first.
1/3 is equivalent to 2/6. 1/2 is equivalent to 3/6. It is still difficult to find the median between the two so I would try 12 as a common denominator.
1/3 is equivalent to 4/12, and 1/2 is equivalent to 6/12. Therefore, the halfway point would be:
5/12