P3 Rectangle and square measurement
find rectilinear perimeter
Find the perimeter of the shown rectilinear figure. Its outer width is 10 cm and outer height is 7 cm; the corner cut-out is 4 cm by 3 cm.
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The pattern behind it: Rectangle and square measurement
Use opposite equal sides, undo the area or perimeter formula, and count each outside edge once.
In this one. For this corner cut-out, the two new edges replace equal parts of the outer rectangle, so the perimeter is unchanged.
How to spot it
Squares tiling a rectangle, or a shape made of several rectangles joined together, point here. The question asks for area, perimeter, or the length of a missing side.
Common mistake
Children multiply length by width when the question actually asks for perimeter. On a composite shape, they add only the labelled sides and miss the ones they must work out themselves.
Try one like it
Standard distinguish area from perimeter The shown 8-by-5 rectangle is covered with square tiles. Does the number of tiles describe its area or its perimeter?The 33 problem patterns
All 33 patterns, one to a page — the 19 behind Primary 5 and 6 word problems, and the skills the younger years are built on. The bar model, how to spot it in the question, and the mistake children make. A booklet you can print. Free.
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