Primary 6 PSLE Mathematics PSLE Revision Quiz

Answer Key: Primary 6 PSLE Mathematics Quiz - Psle Revision

Section A: Multiple-Choice Questions (10 × 2 marks = 20 marks)

1. C) 6

• Working: $\frac{3}{4} \div \frac{1}{8} = \frac{3}{4} \times \frac{8}{1} = \frac{24}{4} = 6$
• Explanation: Dividing by a fraction is the same as multiplying by its reciprocal (flip the second fraction upside down). So, $\frac{3}{4} \div \frac{1}{8}$ becomes $\frac{3}{4} \times \frac{8}{1}$. Multiply the numerators (3 × 8 = 24) and the denominators (4 × 1 = 4), giving $\frac{24}{4}$, which simplifies to 6.
• Common mistake: Some students might multiply the fractions directly without flipping, getting $\frac{3}{32}$.

2. C) $50.00

• Working: 100% - 10% = 90%. The discounted price represents 90% of the original price. So, 90% → $45. 1% → $45 ÷ 90 = $0.50. 100% → $0.50 × 100 = $50.
• Explanation: After a 10% discount, the shirt costs 90% of its original price. Since $45 is 90% of the original, we find 1% by dividing $45 by 90, which gives $0.50. Then, multiply by 100 to find the original price (100%), which is $50.
• Common mistake: A common error is to find 10% of $45 and add it back, which gives $49.50. This is incorrect because the discount is calculated on the original price, not the discounted price.

3. D) 64

• Working: Boys : Girls = 3 : 5. 3 units = 24 boys. 1 unit = 24 ÷ 3 = 8. Total units = 3 + 5 = 8 units. Total students = 8 × 8 = 64.
• Explanation: The ratio 3 : 5 means that for every 3 boys, there are 5 girls. We can think of the class as being divided into 8 equal "units". If 3 units represent 24 boys, then 1 unit is 24 ÷ 3 = 8 students. The total number of students is 8 units × 8 students/unit = 64 students.
• Common mistake: Some students might find the number of girls (5 ×

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Answer Key: Primary 6 PSLE Mathematics Quiz - Psle Revision

Section A: Multiple-Choice Questions (10 × 2 marks = 20 marks)

1. C) 6

• Working: $\frac{3}{4} \div \frac{1}{8} = \frac{3}{4} \times \frac{8}{1} = \frac{24}{4} = 6$
• Explanation: Dividing by a fraction is the same as multiplying by its reciprocal (flip the second fraction upside down). So, $\frac{3}{4} \div \frac{1}{8}$ becomes $\frac{3}{4} \times \frac{8}{1}$. Multiply the numerators (3 × 8 = 24) and the denominators (4 × 1 = 4), giving $\frac{24}{4}$, which simplifies to 6.
• Common mistake: Some students might multiply the fractions directly without flipping, getting $\frac{3}{32}$.

2. C) $50.00

• Working: 100% - 10% = 90%. The discounted price represents 90% of the original price. So, 90% → $45. 1% → $45 ÷ 90 = $0.50. 100% → $0.50 × 100 = $50.
• Explanation: After a 10% discount, the shirt costs 90% of its original price. Since $45 is 90% of the original, we find 1% by dividing $45 by 90, which gives $0.50. Then, multiply by 100 to find the original price (100%), which is $50.
• Common mistake: A common error is to find 10% of $45 and add it back, which gives $49.50. This is incorrect because the discount is calculated on the original price, not the discounted price.

3. D) 64

• Working: Boys : Girls = 3 : 5. 3 units = 24 boys. 1 unit = 24 ÷ 3 = 8. Total units = 3 + 5 = 8 units. Total students = 8 × 8 = 64.
• Explanation: The ratio 3 : 5 means that for every 3 boys, there are 5 girls. We can think of the class as being divided into 8 equal "units". If 3 units represent 24 boys, then 1 unit is 24 ÷ 3 = 8 students. The total number of students is 8 units × 8 students/unit = 64 students.
• Common mistake: Some students might find the number of girls (5 × 8 = 40) and then add it to the boys (24 + 40 = 64) correctly, but others might incorrectly add 3 + 5 = 8 and then multiply by 24, getting 192.

4. B) 8

• Working: $x + 7 = 15$. Subtract 7 from both sides: $x = 15 - 7 = 8$.
• Explanation: To solve for $x$, we need to isolate it. Since 7 is added to $x$, we subtract 7 from both sides of the equation to keep it balanced. This gives $x = 8$.
• Common mistake: Some students might add 7 to 15 instead of subtracting, getting 22.

5. C) 154 cm²

• Working: Area of circle = $\pi r^2 = \frac{22}{7} \times 7 \times 7 = \frac{22}{7} \times 49 = 22 \times 7 = 154$ cm².
• Explanation: The formula for the area of a circle is $\pi r^2$, where $r$ is the radius. Substituting $r = 7$ cm and $\pi = \frac{22}{7}$, we get $\frac{22}{7} \times 7^2 = \frac{22}{7} \times 49$. Since $49 \div 7 = 7$, this simplifies to $22 \times 7 = 154$ cm².
• Common mistake: Some students might use the circumference formula ($2\pi r$) instead, getting 44 cm. Others might forget to square the radius.

6. B) 6 cm

• Working: Volume of cuboid = length × breadth × height. So, $240 = 8 \times 5 \times h$. $8 \times 5 = 40$. $h = 240 \div 40 = 6$ cm.
• Explanation: The volume of a cuboid is found by multiplying its length, breadth, and height. We are given the volume (240 cm³), length (8 cm), and breadth (5 cm). To find the height, we divide the volume by the product of length and breadth: $240 \div (8 \times 5) = 240 \div 40 = 6$ cm.
• Common mistake: Some students might add the dimensions instead of multiplying, or they might divide incorrectly.

7. D) 60

• Working: Average = Total ÷ Number of items. So, Total = Average × Number of items = 15 × 4 = 60.
• Explanation: The average of a set of numbers is found by dividing the total sum by the count of numbers. To find the total, we multiply the average by the count: $15 \times 4 = 60$.
• Common mistake: Some students might divide 15 by 4, getting 3.75, which is incorrect.

8. C) 110°

• Working: In a parallelogram, consecutive angles are supplementary (add up to 180°). So, $\angle BCD = 180^\circ - 70^\circ = 110^\circ$.
• Explanation: In a parallelogram, opposite angles are equal, and adjacent (consecutive) angles are supplementary. Since $\angle ABC$ and $\angle BCD$ are consecutive angles (they share side BC), their sum is 180°. Therefore, $\angle BCD = 180^\circ - 70^\circ = 110^\circ$.
• Common mistake: Some students might think opposite angles are supplementary, or they might assume all angles are equal.

9. B) $5a + 4$

• Working: $3a + 2a + 4 = (3 + 2)a + 4 = 5a + 4$.
• Explanation: We combine like terms. The terms $3a$ and $2a$ both have the variable $a$, so we add their coefficients: $3 + 2 = 5$. The constant term 4 remains unchanged. Thus, the expression simplifies to $5a + 4$.
• Common mistake: Some students might add the 4 to the coefficients, getting $9a$, or they might incorrectly combine $3a$ and $2a$ as $5a^2$.

10. B) 150 km

• Working: Distance = Speed × Time = 60 km/h × 2.5 h = 150 km.
• Explanation: The formula for distance is speed multiplied by time. Substituting the given values: $60 \times 2.5 = 150$ km.
• Common mistake: Some students might multiply incorrectly (e.g., $60 \times 2 = 120$ and forget the 0.5), or they might divide instead of multiply.

Section B: Short-Answer Questions (10 × 3 marks = 30 marks)

11. Answer: $6y$

• Working: $7y - 3y + 2y = (7 - 3 + 2)y = 6y$.
• Explanation: Combine like terms by adding or subtracting their coefficients: $7 - 3 = 4$, then $4 + 2 = 6$. The variable $y$ remains.
• Marking: 1 mark for correct method, 2 marks for correct answer.

12. Answer: 1 : 4

• Working: Convert 1 kg to grams: 1 kg = 1000 g. Ratio = 250 g : 1000 g. Divide both by 250: 250 ÷ 250 = 1, 1000 ÷ 250 = 4. So, the ratio is 1 : 4.
• Explanation: To simplify a ratio, both quantities must be in the same unit. Since 1 kg = 1000 g, the ratio becomes 250 : 1000. Dividing both sides by their greatest common factor (250) gives 1 : 4.
• Marking: 1 mark for converting units, 2 marks for correct simplified ratio.

13. Answer: 44 cm

• Working: Circumference = $\pi \times$ diameter = $\frac{22}{7} \times 14 = 22 \times 2 = 44$ cm.
• Explanation: The circumference of a circle is calculated using the formula $C = \pi d$, where $d$ is the diameter. Substituting $d = 14$ cm and $\pi = \frac{22}{7}$, we get $C = \frac{22}{7} \times 14 = 22 \times 2 = 44$ cm.
• Marking: 1 mark for correct formula, 2 marks for correct answer.

14. Answer: 36,000 cm³ (or 36 litres)

• Working: Volume of tank = 50 × 40 × 30 = 60,000 cm³. Water volume = $\frac{3}{5} \times 60,000 = 36,000$ cm³.
• Explanation: First, find the total volume of the tank by multiplying its dimensions: $50 \times 40 \times 30 = 60,000$ cm³. Since the tank is $\frac{3}{5}$ filled, the water volume is $\frac{3}{5}$ of the total: $\frac{3}{5} \times 60,000 = 36,000$ cm³. (Note: 1 litre = 1000 cm³, so this is 36 litres.)
• Marking: 1 mark for total volume, 1 mark for fraction multiplication, 1 mark for correct answer.

15. Answer: $x = 6$

• Working: $4x - 6 = 18$. Add 6 to both sides: $4x = 24$. Divide both sides by 4: $x = 6$.
• Explanation: To solve for $x$, first isolate the term with $x$ by adding 6 to both sides: $4x = 24$. Then, divide both sides by 4 to get $x = 6$.
• Marking: 1 mark for adding 6, 1 mark for dividing by 4, 1 mark for correct answer.

16. Answer: $24

• Working: Ratio Ahmad : Bala = 2 : 5. Difference in units = 5 - 2 = 3 units. 3 units = $36. 1 unit = $36 ÷ 3 = $12. Ahmad's money = 2 units = 2 × $12 = $24.
• Explanation: The difference in the ratio parts (5 - 2 = 3) corresponds to the actual difference of $36. So, 1 unit = $36 ÷ 3 = $12. Ahmad has 2 units, so he has 2 × $12 = $24.
• Marking: 1 mark for finding the difference in units, 1 mark for finding 1 unit, 1 mark for correct answer.

17. Answer: 48

• Working: Let the original number be $x$. After a 25% increase, the new number is $x + 0.25x = 1.25x$. So, $1.25x = 60$. $x = 60 \div 1.25 = 48$.
• Explanation: A 25% increase means the new number is 125% of the original. So, $1.25 \times$ original = 60. Dividing both sides by 1.25 gives the original number: $60 \div 1.25 = 48$.
• Marking: 1 mark for setting up the equation, 1 mark for correct division, 1 mark for correct answer.

18. Answer: 65°

• Working: In a trapezium, angles on the same side of a leg are supplementary. So, $\angle PQR + \angle QRS = 180^\circ$. Therefore, $\angle QRS = 180^\circ - 115^\circ = 65^\circ$.
• Explanation: Since $PQ$ is parallel to $SR$, the line $QR$ is a transversal. The interior angles on the same side of the transversal ($\angle PQR$ and $\angle QRS$) are supplementary (sum to 180°). Thus, $\angle QRS = 180^\circ - 115^\circ = 65^\circ$.
• Marking: 1 mark for identifying supplementary angles, 1 mark for correct subtraction, 1 mark for correct answer.

19. Answer: 10

• Working: Total of 5 numbers = 5 × 12 = 60. Total of remaining 4 numbers = 60 - 20 = 40. Average of remaining 4 = 40 ÷ 4 = 10.
• Explanation: The average of 5 numbers is 12, so their total is $5 \times 12 = 60$. If one number is 20, the sum of the other 4 is $60 - 20 = 40$. The average of these 4 numbers is $40 \div 4 = 10$.
• Marking: 1 mark for total of 5 numbers, 1 mark for total of remaining 4, 1 mark for correct average.

20. Answer: 875 m²

• Working: Perimeter = 2 × (length + breadth). So, 120 = 2 × (35 + breadth). 60 = 35 + breadth. Breadth = 60 - 35 = 25 m. Area = length × breadth = 35 × 25 = 875 m².
• Explanation: The perimeter of a rectangle is $2(l + b)$. Given the perimeter (120 m) and length (35 m), we first find the breadth: $120 = 2(35 + b)$, so $60 = 35 + b$, giving $b = 25$ m. Then, the area is $l \times b = 35 \times 25 = 875$ m².
• Marking: 1 mark for finding breadth, 1 mark for area formula, 1 mark for correct answer.

END OF ANSWER KEY