Answer:
1 1/2 + (-1/2) is also 1 1/2 - 1/2.
the result is 1 whole, and 1 whole is also the difference between 1 1/2 and 1/2.
Say you have half of a cheese piece, but your friend has 1 whole cheese piece plus half of a cheese piece.
He/She has 1 more cheese piece than you, right? That's the difference between you and your friend's cheese. 1 whole.