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Primary 6 PSLE Mathematics Problem Solving Heuristics Quiz
Free P6 PSLE Maths Problem Solving Heuristics quiz, Exam version, with questions, answers, and PSLE-focused practice for Singapore students.
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Answer Key: Primary 6 PSLE Mathematics Quiz - Problem Solving Heuristics
Total Marks: 50
Section A: Short Answer Questions (Questions 1 to 5)
Each question carries 2 marks.
1.
- Answer: 15 eggs
- Working:
- 3 eggs → 8 cupcakes
- 1 cupcake → 3/8 eggs
- 40 cupcakes → 40 × 3/8 = 15 eggs
- Marking Notes: 1 mark for correct method, 1 mark for correct answer.
- Common Mistake: Students may incorrectly multiply 3 × 5 = 15, but the correct reasoning is unitary method.
2.
- Answer: $12.50
- Working:
- 3 pens → $2.50
- 1 pen → 0.8333...
- 15 pens → 15 × 12.50
- Marking Notes: 1 mark for correct method, 1 mark for correct answer.
- Common Mistake: Students may incorrectly calculate 15 ÷ 3 = 5, then 5 × 12.50. This is also correct.
3.
- Answer: 300 km
- Working:
- Speed = 120 km ÷ 2 h = 60 km/h
- Distance = 60 km/h × 5 h = 300 km
- Marking Notes: 1 mark for correct method, 1 mark for correct answer.
- Teaching Note: This is a direct application of the formula: Distance = Speed × Time.
4.
- Answer: 360 g
- Working:
- 6 people → 240 g
- 1 person → 240 g ÷ 6 = 40 g
- 9 people → 9 × 40 g = 360 g
- Marking Notes: 1 mark for correct method, 1 mark for correct answer.
- Common Mistake: Students may incorrectly add 240 + 120 = 360 g, but the unitary method is more reliable.
5.
- Answer: 120 toys
- Working:
- 3 hours → 45 toys
- 1 hour → 45 ÷ 3 = 15 toys
- 8 hours → 8 × 15 = 120 toys
- Marking Notes: 1 mark for correct method, 1 mark for correct answer.
- Teaching Note: This is a rate problem. The rate is 15 toys per hour.
Section B: Structured Questions (Questions 6 to 10)
Each question carries 3 marks.
6.
- Answer: 58 flowers
- Working:
- First 5 rows: 5 × 8 = 40 flowers
- Next 3 rows: 3 × 6 = 18 flowers
- Total: 40 + 18 = 58 flowers
- Marking Notes: 1 mark for each correct step, 1 mark for final answer.
- Teaching Note: This is a multi-step problem. Break it down into parts.
7.
- Answer: 8 chocolates
- Working:
- Total: 24 chocolates
- Jane takes: 1/3 × 24 = 8 chocolates
- Remaining: 24 - 8 = 16 chocolates
- Brother takes: 1/2 × 16 = 8 chocolates
- Left: 16 - 8 = 8 chocolates
- Marking Notes: 1 mark for each correct step, 1 mark for final answer.
- Common Mistake: Students may incorrectly calculate 1/2 of 24 = 12, forgetting that the brother takes half of the remaining chocolates.
8.
- Answer: $45
- Working:
- Number of bags: 120 ÷ 8 = 15 bags
- Total money: 15 × 45
- Marking Notes: 1 mark for correct number of bags, 1 mark for correct total, 1 mark for final answer.
- Teaching Note: This is a two-step problem. First find the number of bags, then the total money.
9.
- Answer: 15 minutes
- Working:
- Combined rate: 5 + 3 = 8 litres per minute
- Time = 120 litres ÷ 8 litres/min = 15 minutes
- Marking Notes: 1 mark for combined rate, 1 mark for correct method, 1 mark for final answer.
- Teaching Note: When two taps work together, their rates add up.
10.
- Answer: $390
- Working:
- Bus cost: $240
- Entrance fee: 30 × 150
- Total: 150 = $390
- Marking Notes: 1 mark for entrance fee, 1 mark for correct total, 1 mark for final answer.
- Common Mistake: Students may forget to include the bus cost.
Section C: Problem-Solving Questions (Questions 11 to 15)
Each question carries 4 marks.
11.
- Answer: $39.60
- Working:
- Original price: $45
- 20% reduction: 20% of 9
- Sale price: 9 = $36
- 10% increase on sale price: 10% of 3.60
- Final price: 3.60 = $39.60
- Marking Notes: 1 mark for each correct step, 1 mark for final answer.
- Teaching Note: The percentage increase is applied to the sale price, not the original price. This is a common error point.
12.
- Answer: 36 m²
- Working:
- Outer area: 12 m × 8 m = 96 m²
- Inner dimensions: length = 12 - 2 = 10 m, width = 8 - 2 = 6 m
- Inner area: 10 m × 6 m = 60 m²
- Area of path: 96 - 60 = 36 m²
- Marking Notes: 1 mark for outer area, 1 mark for inner dimensions, 1 mark for inner area, 1 mark for final answer.
- Common Mistake: Students may subtract only 1 m from each side instead of 2 m (1 m on each side).
13.
- Answer: 72 red marbles
- Working:
- Red : Blue = 3 : 2 = 6 : 4
- Blue : Green = 4 : 5
- Red : Blue : Green = 6 : 4 : 5
- Green = 60 marbles → 5 units = 60 → 1 unit = 12
- Red = 6 units = 6 × 12 = 72 marbles
- Marking Notes: 1 mark for finding common ratio, 1 mark for finding value of 1 unit, 1 mark for correct answer, 1 mark for clear working.
- Teaching Note: To combine ratios, make the common term (blue) the same in both ratios.
14.
- Answer: 120 km
- Working:
- Let distance = d km
- Time from A to B: d/60 hours
- Time from B to A: d/40 hours
- Total time: d/60 + d/40 = 5
- Common denominator: (2d + 3d)/120 = 5
- 5d/120 = 5
- 5d = 600
- d = 120 km
- Marking Notes: 1 mark for setting up equation, 1 mark for correct algebra, 1 mark for correct answer, 1 mark for clear working.
- Teaching Note: Use the formula Time = Distance ÷ Speed. The total time is the sum of the two times.
15.
- Answer: 12 friends
- Working:
- Let original number of friends = n
- Let original cost per person = $c
- Total cost = n × c
- With 4 more friends: (n + 4)(c - 6) = n × c
- With 3 fewer friends: (n - 3)(c + 8) = n × c
- From first equation: nc - 6n + 4c - 24 = nc → 4c - 6n = 24 → 2c - 3n = 12
- From second equation: nc + 8n - 3c - 24 = nc → 8n - 3c = 24
- Solve simultaneously:
- 2c - 3n = 12 → 2c = 12 + 3n → c = 6 + 1.5n
- Substitute: 8n - 3(6 + 1.5n) = 24
- 8n - 18 - 4.5n = 24
- 3.5n = 42
- n = 12
- Original number of friends = 12
- Marking Notes: 1 mark for setting up equations, 1 mark for correct algebra, 1 mark for correct answer, 1 mark for clear working.
- Teaching Note: This is a challenging problem that requires setting up two equations and solving them simultaneously.
Section D: Challenging Problem-Solving Questions (Questions 16 to 20)
Each question carries 5 marks.
16.
- Answer: $5 profit
- Working:
- Total cost: 200 × 100
- 60% of 200 = 120 eggs sold at 20% profit
- Selling price per egg (profit): 0.60
- Revenue from 120 eggs: 120 × 72
- Remaining: 200 - 120 = 80 eggs sold at 10% loss
- Selling price per egg (loss): 0.45
- Revenue from 80 eggs: 80 × 36
- Total revenue: 36 = $108
- Profit: 100 = $8
- Marking Notes: 1 mark for total cost, 1 mark for revenue from profit eggs, 1 mark for revenue from loss eggs, 1 mark for total revenue, 1 mark for final answer.
- Teaching Note: Profit percentage is calculated on the cost price. A 20% profit means selling price = 120% of cost price.
17.
- Answer: 85.71 litres (or 600/7 litres)
- Working:
- Let capacity = C litres
- Initially: 2/5 C
- After adding 30 litres: 3/4 C
- 3/4 C - 2/5 C = 30
- Common denominator: (15/20 - 8/20)C = 30
- 7/20 C = 30
- C = 30 × 20/7 = 600/7 ≈ 85.71 litres
- Marking Notes: 1 mark for setting up equation, 1 mark for correct algebra, 1 mark for correct answer, 1 mark for clear working, 1 mark for correct units.
- Teaching Note: The difference between the two fractions represents the 30 litres added.
18.
- Answer: Length = 120 m, Speed = 8 m/s
- Working:
- Let length of train = L m, speed = v m/s
- Passing a pole: distance = L, time = 15 s → L = 15v
- Passing a platform: distance = L + 240, time = 45 s → L + 240 = 45v
- Substitute: 15v + 240 = 45v
- 30v = 240
- v = 8 m/s
- L = 15 × 8 = 120 m
- Marking Notes: 1 mark for setting up first equation, 1 mark for setting up second equation, 1 mark for solving, 1 mark for correct speed, 1 mark for correct length.
- Teaching Note: When a train passes a pole, the distance is the length of the train. When it passes a platform, the distance is the length of the train plus the length of the platform.
19.
- Answer: 12 years old
- Working:
- Let son's age = x years
- Man's age = 3x years
- In 12 years: son = x + 12, man = 3x + 12
- 3x + 12 = 2(x + 12)
- 3x + 12 = 2x + 24
- x = 12
- Son is 12 years old now.
- Marking Notes: 1 mark for setting up variables, 1 mark for setting up equation, 1 mark for solving, 1 mark for correct answer, 1 mark for clear working.
- Teaching Note: This is an age problem. The key is to express both ages in terms of the son's current age.
20.
- Answer: 3080 cm³
- Working:
- The longer side (44 cm) becomes the circumference of the base.
- Circumference = 44 cm = 2πr
- 2 × 22/7 × r = 44
- r = 44 × 7 / (2 × 22) = 7 cm
- Height of cylinder = width of paper = 20 cm
- Volume = πr²h = 22/7 × 7² × 20 = 22/7 × 49 × 20 = 22 × 7 × 20 = 3080 cm³
- Marking Notes: 1 mark for identifying circumference, 1 mark for finding radius, 1 mark for correct height, 1 mark for volume formula, 1 mark for final answer.
- Teaching Note: When a rectangular paper is folded to form a cylinder, the longer side becomes the circumference of the base, and the shorter side becomes the height.