Primary 6 PSLE Mathematics Whole Numbers Quiz

Primary 6 PSLE Mathematics Quiz - Whole Numbers - Answer Key

Total Marks: 40

Section A: Multiple-Choice Questions (5 marks)

1. (D) 7 000 000

• Marks: 1
• Explanation: The number is 5 078 241. The digit 7 is in the millions place. The value of a digit depends on its place value. The place values from right to left are: ones, tens, hundreds, thousands, ten thousands, hundred thousands, millions. The 7 is in the millions place, so its value is 7 000 000.
• Common Mistake: Choosing (C) 70 000, which is the value of 7 in the ten-thousands place.

2. (A) 6

• Marks: 1
• Explanation: Factors of 48: 1, 2, 3, 4, 6, 8, 12, 16, 24, 48. Multiples of 4: 4, 8, 12, 16, 20, 24, ... From the factors of 48, the numbers that are not multiples of 4 are 1, 2, 3, 6. Among the options, only 6 fits.
• Common Mistake: Choosing 8 or 12, which are both factors of 48 and multiples of 4.

3. (B) 350 000

• Marks: 1
• Explanation: To round to the nearest thousand, look at the hundreds digit. The number is 349 857. The hundreds digit is 8, which is 5 or more, so we round up the thousands digit. The thousands digit is 9, rounding up makes it 10, so we carry over to the ten-thousands place. 349 857 rounded to the nearest thousand is 350 000.
• Common Mistake: Forgetting to carry over when the digit is 9.

4. (C) 28

• Marks: 1
• Explanation: Prime numbers are numbers greater than 1 that have only two factors: 1 and themselves. The first 5 prime numbers are 2, 3, 5, 7, 11. Their sum is 2 + 3 + 5 + 7 + 11 = 28.
• Common Mistake: Including 1 as a prime number. 1 is not a prime number.

5. (B) 38

• Marks: 1
• Explanation: The baker has 450 eggs. Each tray holds 12 eggs. Number of trays needed = 450 ÷ 12 = 37.5. Since he cannot use half a tray, he needs 38 trays to pack all the eggs. 37 trays would only hold 37 × 12 = 444 eggs, leaving 6 eggs unpacked.
• Common Mistake: Choosing 37.5 or 37 without considering the real-world context of needing a whole number of trays.

Section B: Short-Answer Questions (20 marks)

6. Three million five hundred thousand.

• Marks: 2
• Explanation: The number 3 500 000 is read as "three million five hundred thousand". The digit 3 is in the millions place, and the digit 5 is in the hundred-thousands place.
• Marking Note: Award 1 mark for "three million" and 1 mark for "five hundred thousand". Spelling errors are acceptable if the meaning is clear.

7. 600

• Marks: 2
• Explanation: 15 000 ÷ 25 = 600. This can be calculated by thinking of 15 000 as 15 × 1000, and 25 as 5 × 5. 15 000 ÷ 25 = (15 000 ÷ 5) ÷ 5 = 3 000 ÷ 5 = 600.
• Working: 15 000 ÷ 25 = 600

8. 1, 2, 3, 6

• Marks: 2
• 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.
• Marking Note: Award 1 mark for listing at least 3 correct common factors. Award full marks for all 4 correct factors.

9. 10 259

• Marks: 2
• Explanation: To form the smallest 5-digit number, arrange the digits in ascending order from left to right. The smallest digit is 0, but 0 cannot be the first digit of a 5-digit number. So, the smallest non-zero digit (1) goes first. Then arrange the remaining digits (0, 2, 5, 9) in ascending order: 0, 2, 5, 9. The smallest number is 10 259.
• Common Mistake: Placing 0 first, resulting in a 4-digit number like 01 259, which is not a 5-digit number.

10. 73 500

• Marks: 2
• Explanation: Number of toy cars produced in 30 days = 2 450 × 30 = 73 500.
• Working: 2 450 × 30 = 2 450 × 3 × 10 = 7 350 × 10 = 73 500

11. 31 668

• Marks: 2
• Explanation: 406 × 78 = 406 × (80 - 2) = 406 × 80 - 406 × 2 = 32 480 - 812 = 31 668.
• Working:

    406
  ×  78
  -----
   3248  (406 × 8)
  28420  (406 × 70)
  -----
  31668
  

12. 1 123

• Marks: 2
• Explanation: The number = (divisor × quotient) + remainder = (9 × 124) + 7 = 1 116 + 7 = 1 123.
• Working: (9 × 124) + 7 = 1 116 + 7 = 1 123

13. 8 999

• Marks: 2
• Explanation: The largest 4-digit number is 9 999. The smallest 4-digit number is 1 000. The difference is 9 999 - 1 000 = 8 999.
• Working: 9 999 - 1 000 = 8 999

14. 160 sweets

• Marks: 2
• Explanation: Total sweets bought = 8 × 35 = 280. Sweets left = 280 - 120 = 160.
• Working: 8 × 35 = 280. 280 - 120 = 160.

15. 510 km

• Marks: 2
• Explanation: Distance = Speed × Time = 85 km/h × 6 h = 510 km.
• Working: 85 × 6 = 510

Section C: Problem-Solving Questions (20 marks)

16. 4 500 books

• Marks: 4
• Explanation: Total books = 1 250 + 1 500 + 1 750 = 4 500.
• Working:
  • 1 250 + 1 500 = 2 750
  • 2 750 + 1 750 = 4 500
• Marking Scheme:
  • 1 mark for correct method (adding all three numbers)
  • 2 marks for correct intermediate addition
  • 1 mark for correct final answer

17. $360

• Marks: 4
• Explanation:
  • Step 1: Find the number of boxes. 240 muffins ÷ 8 muffins/box = 30 boxes.
  • Step 2: Find the total money collected. 30 boxes × $12/box =$360.
• Working:
  • 240 ÷ 8 = 30
  • 30 × 12 = 360
• Marking Scheme:
  • 1 mark for correct method to find number of boxes
  • 1 mark for correct number of boxes (30)
  • 1 mark for correct method to find total money
  • 1 mark for correct final answer ($360)

18. 625 chairs each, 0 chairs left over

• Marks: 4
• Explanation:
  • Step 1: Divide the total chairs by the number of schools. 5 000 ÷ 8 = 625.
  • Step 2: Check the remainder. 625 × 8 = 5 000. There is no remainder.
• Working:
  • 5 000 ÷ 8 = 625 R 0
• Marking Scheme:
  • 1 mark for correct division method
  • 1 mark for correct quotient (625)
  • 1 mark for correct remainder (0)
  • 1 mark for stating both answers in context

19. 2 100 chickens

• Marks: 4
• Explanation:
  • Step 1: Find the number of chickens after selling. 2 450 - 1 200 = 1 250.
  • Step 2: Find the number of chickens after buying. 1 250 + 850 = 2 100.
• Working:
  • 2 450 - 1 200 = 1 250
  • 1 250 + 850 = 2 100
• Marking Scheme:
  • 1 mark for correct method for subtraction
  • 1 mark for correct intermediate answer (1 250)
  • 1 mark for correct method for addition
  • 1 mark for correct final answer (2 100)

20. 12 000 bottles, 48 boxes

• Marks: 4
• Explanation:
  • Step 1: Find the total bottles produced in 8 hours. 1 500 bottles/hour × 8 hours = 12 000 bottles.
  • Step 2: Find the number of boxes needed. 12 000 bottles ÷ 250 bottles/box = 48 boxes.
• Working:
  • 1 500 × 8 = 12 000
  • 12 000 ÷ 250 = 48
• Marking Scheme:
  • 1 mark for correct method to find total bottles
  • 1 mark for correct total bottles (12 000)
  • 1 mark for correct method to find number of boxes
  • 1 mark for correct final answer (48 boxes)

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