Primary 6 PSLE Mathematics Whole Numbers Quiz

Primary 6 PSLE Mathematics Quiz - Whole Numbers - Answer Key

Total Marks: 40

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Section A: Multiple-Choice Questions (Questions 1 to 5)

1 mark each

1. D) 70 000

• Explanation: In the number 4 078 213, the digit 7 is in the ten-thousands place. The place value of the ten-thousands place is 10 000. So, the value of the digit 7 is 7 × 10 000 = 70 000.
• Common Mistake: Students might confuse place value with the digit itself and choose A) 7, or misidentify the place as thousands and choose C) 7000.

2. C) 24

• Explanation: A multiple of a number is the product of that number and a whole number. We need a number that is a multiple of both 6 and 8. Let's check the options:
  • 12 is a multiple of 6 (6 × 2 = 12) but not of 8 (8 × 1.5 = 12, not a whole number).
  • 16 is a multiple of 8 (8 × 2 = 16) but not of 6.
  • 24 is a multiple of 6 (6 × 4 = 24) and of 8 (8 × 3 = 24).
  • 36 is a multiple of 6 (6 × 6 = 36) but not of 8.
• Key Concept: A common multiple is a number that is a multiple of two or more numbers.

3. D) 3 500 000

• Explanation: To round to the nearest hundred thousand, we look at the ten-thousands digit. The number is 3 456 789. The hundred-thousands digit is 4. The ten-thousands digit is 5. Since the ten-thousands digit is 5 or more, we round up the hundred-thousands digit. So, 4 becomes 5, and all digits to the right become 0. The answer is 3 500 000.
• Common Mistake: Students might round to the nearest ten thousand (3 460 000) or forget to change the digits to the right.

4. A) 10 200

• Explanation: 408 × 25 = 408 × (100 ÷ 4) = (408 × 100) ÷ 4 = 40 800 ÷ 4 = 10 200. Alternatively, 408 × 20 = 8160, 408 × 5 = 2040, 8160 + 2040 = 10 200.
• Key Concept: Multiplication of whole numbers.

5. A) 37

• Explanation: This is a division problem with a remainder. 450 ÷ 12 = 37 remainder 6. The baker can pack 37 full trays of 12 eggs each. The remaining 6 eggs are not enough for a full tray.
• Common Mistake: Students might give the answer as 37.5 (the decimal result) or round up to 38, not understanding the context of "full trays".

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Section B: Short-Answer Questions (Questions 6 to 15)

2 marks each (1 mark for correct method, 1 mark for correct answer)

6. 8 406 030

• Explanation: Write the number in a place value chart.
  • Millions: 8
  • Hundred Thousands: 4
  • Ten Thousands: 0
  • Thousands: 6
  • Hundreds: 0
  • Tens: 3
  • Ones: 0 So, the number is 8 406 030.

7. 765 433

• Explanation: 1 000 000 – 234 567 = 765 433.

    1 000 000
  -   234 567
  -----------
    765 433
  

  We need to borrow across multiple zeros. 1 000 000 = 999 999 + 1. So, 999 999 – 234 567 = 765 432, then add 1 = 765 433.

8. 28

• Explanation: The first 5 prime numbers are 2, 3, 5, 7, and 11. Their sum is 2 + 3 + 5 + 7 + 11 = 28.
• Key Concept: A prime number is a whole number greater than 1 that has only two factors: 1 and itself.

9. 68 600

• Explanation: Number of toys produced in 28 days = 2 450 × 28.
  • 2 450 × 20 = 49 000
  • 2 450 × 8 = 19 600
  • 49 000 + 19 600 = 68 600

10. 1, 2, 3, 6

• Explanation: Factors of 18: 1, 2, 3, 6, 9, 18. Factors of 30: 1, 2, 3, 5, 6, 10, 15, 30. Common factors are numbers that appear in both lists: 1, 2, 3, 6.

11. 7000

• Explanation: 56 × 1000 ÷ 8 = 56 000 ÷ 8 = 7000. Alternatively, 56 ÷ 8 × 1000 = 7 × 1000 = 7000.

12. 1111

• Explanation: The number = (divisor × quotient) + remainder = (9 × 123) + 4 = 1107 + 4 = 1111.

13. 1035

• Explanation: A number divisible by 5 ends in 0 or 5. A number divisible by 9 has a sum of digits divisible by 9. The smallest 4-digit number is 1000. Let's check numbers ending in 0 or 5 starting from 1000.
  • 1000: sum of digits = 1, not divisible by 9.
  • 1005: sum of digits = 6, not divisible by 9.
  • 1010: sum = 2.
  • 1015: sum = 7.
  • 1020: sum = 3.
  • 1025: sum = 8.
  • 1030: sum = 4.
  • 1035: sum = 1+0+3+5 = 9, divisible by 9. And it ends in 5, so it is divisible by 5. Therefore, 1035 is the smallest 4-digit number divisible by both 5 and 9.

14. 20

• Explanation: Total weight of rice = 5 × 8 kg = 40 kg. Number of 2 kg packets = 40 kg ÷ 2 kg/packet = 20 packets.

15. 54

• Explanation: Let the smaller number be 1 unit. The larger number is 6 units. The difference is 6 units – 1 unit = 5 units. 5 units = 45. 1 unit = 45 ÷ 5 = 9. The larger number is 6 units = 6 × 9 = 54.

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Section C: Problem-Solving Questions (Questions 16 to 20)

3 marks each (1 mark for correct method/working, 1 mark for correct intermediate steps, 1 mark for correct final answer)

16. 12 375 bottles

• Explanation:
  1. Bottles sold in January: 3 680
  2. Bottles sold in February: 3 680 + 1 245 = 4 925
  3. Bottles sold in March: 4 925 – 2 100 = 2 825
  4. Total bottles sold: 3 680 + 4 925 + 2 825 = 12 375
• Marking Notes: Award 1 mark for correctly finding February's sales, 1 mark for correctly finding March's sales, and 1 mark for the correct total.

17. 24 blue marbles

• Explanation: Let the number of blue marbles be 1 unit. Red marbles = 3 units. Green marbles = 1 unit + 12. Total marbles = 3 units + 1 unit + 1 unit + 12 = 5 units + 12. 5 units + 12 = 132 5 units = 132 – 12 = 120 1 unit = 120 ÷ 5 = 24 Therefore, there are 24 blue marbles.
• Marking Notes: Award 1 mark for setting up the correct relationship (e.g., using units), 1 mark for forming the equation, and 1 mark for the correct answer.

18. 153 km

• Explanation:
  1. Distance travelled by bus = speed × time = 75 km/h × 2 h = 150 km.
  2. Total distance = distance by bus + distance walked = 150 km + 3 km = 153 km.
• Marking Notes: Award 1 mark for correctly calculating the bus distance, 1 mark for adding the walking distance, and 1 mark for the correct answer with unit (km).

19. 398 m

• Explanation:
  1. Perimeter of the field = 2 × (length + width) = 2 × (120 m + 85 m) = 2 × 205 m = 410 m.
  2. Total width of the 4 gates = 4 × 3 m = 12 m.
  3. Total length of the fence = perimeter of field – total width of gates = 410 m – 12 m = 398 m.
• Marking Notes: Award 1 mark for correctly calculating the perimeter, 1 mark for subtracting the gate widths, and 1 mark for the correct answer with unit (m).

20. 37 loaves

• Explanation:
  1. Flour per loaf = 2 kg ÷ 5 loaves = 0.4 kg/loaf.
  2. Number of loaves from 15 kg = 15 kg ÷ 0.4 kg/loaf = 37.5 loaves.
  3. Since he cannot make half a loaf, he can make 37 whole loaves.
• Alternative Method (Unitary): 2 kg of flour → 5 loaves 1 kg of flour → 5 ÷ 2 = 2.5 loaves 15 kg of flour → 15 × 2.5 = 37.5 loaves. He can make 37 loaves.
• Marking Notes: Award 1 mark for a correct method to find the number of loaves, 1 mark for recognising that only whole loaves can be made, and 1 mark for the correct answer (37, not 37.5).