There are 8 shaded pieces in the first square and 7 shaded pieces in the second square.
Move shaded pieces from the second square to the first square until it is filled.
Leave the remaining pieces in the second square.

	+		=
1	+	0.5	=	1.5

There are 63 shaded pieces in the first grid.
Since there are 52 shaded squares in the second grid, remove 52 shaded squares from the first grid.

	=
		0.11

So, 0.63 - 0.52 = 0.11.