Area and Perimeter
The most common mistakes Singapore primary students make in Area and Perimeter, distilled from 56+ MOE-aligned questions across P3, P4. Free practice at every level.
Top 10 mistakes in Area and Perimeter
- #1Misconception
That is area.
- #2Partial logic
Right number, wrong unit.
- #3Misconception
Added only one length and one width: 12 + 8 = 20. Forgot that perimeter goes all the way around — a rectangle has two lengths and two widths.
- #4Calc error
Added all four sides but used 16 instead of 8 for the second width: 12 + 8 + 12 + 16 = 48.
- #5Misconception
Multiplied length × width to find area instead of perimeter: 12 × 8 = 96. The question asks for the distance around (perimeter), not the space inside (area).
- #6Partial logic
Student divided the remaining area 84 by the length 12 to find a width of 7 cm, then subtracted from 10 to get the square side: 10 - 7 = 3 cm. This incorrectly treats the L-shape as a simple rectangle.
- #7Misconception
Student took the square root of the remaining area instead of the removed area: sqrt(84) = approx 9.2, rounded to 9 cm.
- #8Misconception
Student correctly found the removed area = 120 - 84 = 36 cm2, but reported the area value (36) as the side length instead of finding the square root.
- #9Misconception
42 cm is not correct. Check whether removing the corner notch actually changes the total perimeter — the two removed outer edges are replaced by two equal inner edges.
- #10Misconception
46 cm is too large. You may have added the notch edges on top of the original perimeter. When a corner notch is cut, the two new inner edges (3 cm and 4 cm) exactly replace the two outer edges that were removed, so the total perimeter stays the same.
Practise Area and Perimeter by level
- Primary 328 questions
- Primary 428 questions
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