probability on a set of numbers

Two numbers a and b, are randomly selected without replacement from the set {2,3,4,5,6}. What is the probability that the fraction a/b is less than 1 and can be expressed as a decimal? Express answer in a fraction.

My approach to this problem is:

totally there are 5 numbers and once a number is taken from the set, it is not put back. So with one selection(1/5), two numbers have gone and so, for the second 1/3 and what about the remaing one number. I am afraid my approach is totally wrong.

Please guide me.

Thanks,