Question P4–P5 Overlap and cancel
Two different squares overlap in an unshaded square. Their full width is 10 cm, and shaded area A is 24 cm² greater than shaded area B. Find the unshaded area.
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Two shapes share a region, and the shared part cancels out.
In this one. The overlap sits inside both squares, so taking it off both cancels it — the difference of the shaded parts is just the difference of the whole squares.
Shapes are joined, stacked, or have a piece cut off, and the question compares a perimeter or length before and after, rather than asking for an area from scratch.
Children assume perimeter changes the same way area does. Joining shapes or cutting off a corner can leave the perimeter unchanged, or change it by a different amount from the area.
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