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PSLE 2020 · Paper 2 · Q5 Measurement & Geometry · Area & perimeter 2 marks · open-ended difficulty 3 of 5

PSLE 2020 Paper 2, Question 5: Area & perimeter

The answer

300 cm²

PSLE 2020 Paper 2 Question 5 · Verified worked solution by the Genius Plus Academy teaching team

What this question tests

This is Question 5 of the PSLE 2020 Paper 2 Mathematics paper. It tests area & perimeter, in the Measurement & Geometry strand. It is worth 2 marks. Open your copy of the paper at this question, then follow our full worked solution below.

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Video: a Genius Plus Academy teacher solving PSLE 2020 Paper 2 Question 5

Teacher video · 2020 P2 Q5

Step-by-step solution

Square split into top half (20u, yellow) and bottom half (20u, blue) with the shaded strips visible, beside the unit working 22u → 165, 40u → 300 — GPA worked solution: the square split into two 20u halves; shaded = 12u + 10u = 22u = 165 cm², so 40u = 300 cm².

Shaded fraction \(= \dfrac{3}{5} \times \dfrac{1}{2} + \dfrac{2}{4} \times \dfrac{1}{2} = \dfrac{3}{10} + \dfrac{1}{4} = \dfrac{11}{20}\) of the square. So \(\dfrac{11}{20}\) of the area \(= 165\) cm² \(\Rightarrow \dfrac{1}{20} = 15\) cm² \(\Rightarrow\) area \(= 15 \times 20 = 300\) cm².

Answer: 300 cm²

Same structure, different costume

A question is hard because of its structure, not its story.

Change egg tarts to badges, a tank to two tanks, a ring of card to a folded sheet, and a child sees a brand new problem. The lock underneath is the same, and so is the key. Once a student can name the structure, a whole row of questions that look different start to open the same way.

It is also where marks really leak. Across fourteen years of papers, the marks lost in PSLE math leak at the reading far more than at the arithmetic, which is exactly why recognising the structure fixes them. We call this Lock and Key: name the lock, then the key follows.

See what the paper rewards → The hardest questions, shown working →

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