To solve this expression, we need to simplify each fraction separately and then perform the addition.

First, let's simplify the fractions:
-1/5 + 2/5 = 1/5
1/2 + -3/2 = -2/2 = -1

Now, let's add the simplified fractions:
1/5 + (-1) = 1/5 - 1 = 1/5 - 5/5 = (1 - 5)/5 = -4/5

Therefore, -1/5 + 2/5 : 1/2 + -3/2 = -4/5.