Watch the walkthrough
Teacher video · 2015 P2 Q15
The answer
(a) \(0.8\) ℓ (b) \(8.1\) ℓ
PSLE 2015 Paper 2 Question 15 · Verified worked solution by the Genius Plus Academy teaching team
What this question tests
This is Question 15 of the PSLE 2015 Paper 2 Mathematics paper. It tests volume, in the Measurement & Geometry strand. It is worth 4 marks: 1 + 3. Open your copy of the paper at this question, then follow our full worked solution below.
Watch the walkthrough
Teacher video · 2015 P2 Q15
(a) With the same remaining drink, a large bottle is 0.5 ℓ too much and a small bottle leaves 0.3 ℓ over, so large \(-\) small \(= 0.5 + 0.3 = 0.8\) ℓ.
(b) \(3L + 5S = 7.2\): replace each \(L\) with \(S + 0.8\): \(8S + 2.4 = 7.2\), so \(S = 0.6\) ℓ (and \(L = 1.4\) ℓ). Total made \(= 7.2 + 0.6 + 0.3 = 8.1\) ℓ. Check: after 7.2 ℓ, drink left \(= 0.6 + 0.3 = 0.9\) ℓ; a large bottle (1.4 ℓ) is indeed 0.5 ℓ short ✓.
Answer: (a) \(0.8\) ℓ (b) \(8.1\) ℓ
Same structure, different costume
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.
Want more questions like this, with worked solutions?
We will send a set to practise. One email, no spam.
Same skill, different years. Each has a verified worked solution.
One of the 10 question types
The PSLE keeps testing the same 10 structures. Our PSLE Math Intensive trains the Lock and Key reflex across all ten, with 158 curated questions over two days.
It is a volume question from the Measurement & Geometry strand, worth 4 marks: 1 + 3.
Yes. A Genius Plus Academy teacher works it on video above, free to watch.
Yes. Every worked solution here is free to read, with no sign-up wall.
Browse every year from 2014 to 2025 in our worked-solutions library at /resources/solutions/psle/.
Book a free trial and diagnostic. We will look at a real paper and show you exactly where the marks are going.