Four identical rectangles, each 7 cm long and 4 cm wide, are placed side by side, joined along their 7 cm edges, to form one long rectangle with no gaps or overlaps.
- What is the length of the whole long rectangle?
- What is the perimeter of the whole long rectangle?
Need a hint?
Only the outer edges count for the perimeter. Work out the length of the whole shape first, then add its two lengths and two widths.
Worked answer
- (a) Four widths of 4 cm lie end to end: 4 × 4 = 16 cm.
- (b) The whole shape is 16 cm long and 7 cm wide.
- (b) Perimeter = 2 × (16 + 7) = 2 × 23 = 46 cm.
Answer: 46 cm
The mistake this question tests
Habit
Area and perimeter formulas
Pupils add the perimeters of all four rectangles (4 × 22 = 88 cm), which counts the joined edges twice.
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