PSLE 2018 Paper 2 Q10 Worked Solution

Step-by-step solution

Handwritten front view (column 3 tall with one square at bottom right) and side view (columns 2, 1, 3 tall) — GPA worked solution, part (a): Front view, an L 3 squares tall with 1 square to the right at the bottom; Side view, bottom row of 3 with a 2-stack at one end and a 3-stack at the other.

(a) Front view: column heights [3, 1]. Side view: column heights [2, 1, 3]. (The worked-on paper draws the same views.)

(b) FLAG, sources disagree with independent solution. Every GPA source (handwritten key, rescans, docx, worked-on paper) gives 6. Independent re-solving: with the whole outside (including the base) painted, a cube has exactly four faces painted exactly when it is glued to exactly 2 other cubes. Reconstructing the solid from the answer views (one row holding a front 2-stack, a single middle cube and a back 3-column; the adjacent row holding two single cubes; 2+1+3+1+1 = 8): the cubes glued to exactly 2 others are the 3-column's base cube, the 3-column's middle cube, and the two single cubes of the adjacent row, 4 cubes. The tops of the 3-column and of the 2-stack are glued to only 1 cube each, so they have five painted faces; the 2-stack's bottom cube and the single middle cube are glued to 3, so they have three. Therefore: exactly four → 4 cubes; at least four → 6 cubes. The GPA answer of 6 matches the "at least four" count (it appears to include the two 5-face cubes). Recorded as a discrepancy; the GPA answer 6 is reproduced above, but re-check against the official SEAB key before teaching this part.

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.

Questions students ask

What does PSLE 2018 Paper 2 Question 10 test?

It is a geometry (properties of shapes) question from the Measurement & Geometry strand, worth 3 marks: 2 + 1.

Is there a video solution?

Not yet for this question. The full written solution is above, and we are filming Paper 2 walkthroughs steadily.

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PSLE 2018 Paper 2, Question 10: Geometry (properties of shapes)

Step-by-step solution

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

More geometry (properties of shapes) questions, worked the same way

Read a question, know the method.

Questions students ask

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