Question P4–P5–P6 Overlap and cancel
Five identical semicircles sit on one straight line — three above it, two below.
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Two shapes share a region, and the shared part cancels out.
In this one. Cancel the shared overlap: what is left of two equal lengths must be equal too.
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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