Question 976042
If we think of this as a grid 4x5, there are 20 spaces.

5/20 he gets a drink

4/20 he gets ice cream

2/20, both.

So there are really just 7 outcomes that have a purchase. 3 drink only, 2 both, 2 ice cream only. 

If he bought at least 1, he is in the space of these 7, and has a 2/7 chance he bought both.