Primary 3 Mathematics Addition Subtraction Quiz

Primary 3 Mathematics Quiz - Addition Subtraction (Answer Key)

Total Marks: 40

Section A: Mental Calculation (Questions 1 - 5)

(2 marks each)

1. 45 + 37 = 82

• Marks: 1 mark for correct method (e.g., 45 + 30 = 75, 75 + 7 = 82), 1 mark for correct answer.
• Explanation: Add the tens: 40 + 30 = 70. Add the ones: 5 + 7 = 12. Then add the results: 70 + 12 = 82.
• Common mistake: Forgetting to regroup when adding ones (5 + 7 = 12, not 12 ones but 1 ten and 2 ones).

2. 82 - 56 = 26

• Marks: 1 mark for correct method (e.g., 82 - 50 = 32, 32 - 6 = 26), 1 mark for correct answer.
• Explanation: Subtract the tens: 80 - 50 = 30. Subtract the ones: 2 - 6 cannot be done, so regroup: 82 = 70 + 12. Then 12 - 6 = 6. So 70 + 6 = 76? No, careful: 82 - 56 = (80 - 50) + (2 - 6) = 30 + (-4) = 26. Better: 82 - 50 = 32, then 32 - 6 = 26.
• Common mistake: Subtracting the smaller digit from the larger without regrouping (e.g., 82 - 56 = 34).

3. 290 + 450 = 740

• Marks: 1 mark for correct method, 1 mark for correct answer.
• Explanation: Add the hundreds: 200 + 400 = 600. Add the tens: 90 + 50 = 140. Then add the results: 600 + 140 = 740.
• Common mistake: Forgetting to regroup the tens (90 + 50 = 140, which is 1 hundred and 4 tens).

4. 700 - 320 = 380

• Marks: 1 mark for correct method, 1 mark for correct answer.
• Explanation: Subtract the hundreds: 700 - 300 = 400. Subtract the tens: 0 - 20 cannot be done, so regroup: 700 = 600 + 100. Then 100 - 20 = 80. So 600 + 80 = 680? No, careful: 700 - 320 = (700 - 300) - 20 = 400 - 20 = 380.
• Common mistake: Subtracting 320 from 700 without regrouping (e.g., 700 - 320 = 420).

5. 125 + 98 = 223 ice creams

• Marks: 1 mark for correct method (addition), 1 mark for correct answer with unit.
• Explanation: Add the hundreds: 100 + 0 = 100. Add the tens: 20 + 90 = 110. Add the ones: 5 + 8 = 13. Then add the results: 100 + 110 + 13 = 223.
• Common mistake: Forgetting to regroup the tens (20 + 90 = 110, which is 1 hundred and 1 ten).

Section B: Written Calculation (Questions 6 - 10)

(2 marks each)

6. 2345 + 1678 = 4023

• Marks: 1 mark for correct method (vertical addition with regrouping), 1 mark for correct answer.
• Explanation:

    2345
  + 1678
  ------
    4023
  

  Ones: 5 + 8 = 13, write 3, carry 1. Tens: 4 + 7 + 1 = 12, write 2, carry 1. Hundreds: 3 + 6 + 1 = 10, write 0, carry 1. Thousands: 2 + 1 + 1 = 4.
• Common mistake: Forgetting to add the carried digit.

7. 5000 - 2345 = 2655

• Marks: 1 mark for correct method (vertical subtraction with regrouping), 1 mark for correct answer.
• Explanation:

    5000
  - 2345
  ------
    2655
  

  Regroup: 5000 = 4000 + 1000. Then 1000 = 900 + 100. Then 100 = 90 + 10. So 5000 = 4000 + 900 + 90 + 10. Subtract: 10 - 5 = 5, 90 - 40 = 50, 900 - 300 = 600, 4000 - 2000 = 2000. Total: 2000 + 600 + 50 + 5 = 2655.
• Common mistake: Forgetting to regroup across multiple zeros.

8. 3760 + 1250 = 5010

• Marks: 1 mark for correct method, 1 mark for correct answer.
• Explanation:

    3760
  + 1250
  ------
    5010
  

  Ones: 0 + 0 = 0. Tens: 6 + 5 = 11, write 1, carry 1. Hundreds: 7 + 2 + 1 = 10, write 0, carry 1. Thousands: 3 + 1 + 1 = 5.
• Common mistake: Forgetting to add the carried digit.

9. 4000 - 1899 = 2101

• Marks: 1 mark for correct method, 1 mark for correct answer.
• Explanation:

    4000
  - 1899
  ------
    2101
  

  Regroup: 4000 = 3000 + 1000. Then 1000 = 900 + 100. Then 100 = 90 + 10. So 4000 = 3000 + 900 + 90 + 10. Subtract: 10 - 9 = 1, 90 - 90 = 0, 900 - 800 = 100, 3000 - 1000 = 2000. Total: 2000 + 100 + 0 + 1 = 2101.
• Common mistake: Forgetting to regroup across multiple zeros.

10. 456 + 789 + 123 = 1368

• Marks: 1 mark for correct method, 1 mark for correct answer.
• Explanation:

    456
    789
  + 123
  -----
   1368
  

  Ones: 6 + 9 + 3 = 18, write 8, carry 1. Tens: 5 + 8 + 2 + 1 = 16, write 6, carry 1. Hundreds: 4 + 7 + 1 + 1 = 13, write 3, carry 1. Thousands: 1.
• Common mistake: Forgetting to add the carried digit.

Section C: Word Problems (Questions 11 - 15)

(3 marks each)

11. Total balloons: 3500 + 2800 = 6300. Balloons left: 6300 - 1200 = 5100.

• Marks: 1 mark for finding total balloons, 1 mark for subtracting used balloons, 1 mark for correct answer with unit.
• Explanation: First, find the total number of balloons: 3500 + 2800 = 6300. Then, subtract the balloons used: 6300 - 1200 = 5100.
• Common mistake: Only subtracting from one colour instead of the total.

12. Pages read: 89 + 127 = 216. Pages left: 245 - 216 = 29.

• Marks: 1 mark for finding total pages read, 1 mark for subtracting from total, 1 mark for correct answer with unit.
• Explanation: First, find the total number of pages Sam read: 89 + 127 = 216. Then, subtract from the total pages: 245 - 216 = 29.
• Common mistake: Adding the pages read to the total instead of subtracting.

13. Total apples sold: 1780 + 1560 = 3340. Apples not sold: 4500 - 3340 = 1160.

• Marks: 1 mark for finding total apples sold, 1 mark for subtracting from total, 1 mark for correct answer with unit.
• Explanation: First, find the total number of apples sold: 1780 + 1560 = 3340. Then, subtract from the total apples: 4500 - 3340 = 1160.
• Common mistake: Subtracting only one batch of sold apples.

14. Difference: 2340 - 1980 = 360.

• Marks: 1 mark for identifying subtraction, 1 mark for correct method, 1 mark for correct answer with unit.
• Explanation: "How many more" means subtraction. Subtract the number of girls from the number of boys: 2340 - 1980 = 360.
• Common mistake: Adding instead of subtracting.

15. Total cookies packed: 1560 - 8 = 1552. Boxes packed: 1552 ÷ 12 = 129 R 4. So 129 boxes.

• Marks: 1 mark for finding cookies packed, 1 mark for correct division, 1 mark for correct answer with unit.
• Explanation: First, find the number of cookies that were packed into boxes: 1560 - 8 = 1552. Then, divide by the number of cookies per box: 1552 ÷ 12 = 129 remainder 4. So, 129 boxes were packed.
• Common mistake: Forgetting to subtract the leftover cookies before dividing.

Section D: Problem Solving (Questions 16 - 20)

(4 marks each)

16. After unloading: 3500 - 1780 = 1720 kg. After adding: 1720 + 950 = 2670 kg.

• Marks: 1 mark for subtracting unloaded sand, 1 mark for correct answer after first step, 1 mark for adding new sand, 1 mark for correct final answer with unit.
• Explanation: First, subtract the sand that was unloaded: 3500 - 1780 = 1720 kg. Then, add the sand that was added: 1720 + 950 = 2670 kg.
• Common mistake: Adding the unloaded sand instead of subtracting.

17. After Monday: 5000 - 1250 = 3750. After Tuesday: 3750 - 980 = 2770. After delivery: 2770 + 2000 = 4770.

• Marks: 1 mark for each correct step, 1 mark for correct final answer with unit.
• Explanation: First, subtract Monday's sales: 5000 - 1250 = 3750. Then, subtract Tuesday's sales: 3750 - 980 = 2770. Then, add the new delivery: 2770 + 2000 = 4770.
• Common mistake: Adding the sales instead of subtracting.

18. Total books: 450 + 380 + 520 = 1350. Books left: 1350 - 200 = 1150.

• Marks: 1 mark for finding total books, 1 mark for correct addition, 1 mark for subtracting borrowed books, 1 mark for correct final answer with unit.
• Explanation: First, find the total number of books: 450 + 380 + 520 = 1350. Then, subtract the borrowed books: 1350 - 200 = 1150.
• Common mistake: Forgetting to add all three shelves.

19. After supermarket: 6000 - 2450 = 3550. After restaurant: 3550 - 1890 = 1660. After collection: 1660 + 1500 = 3160.

• Marks: 1 mark for each correct step, 1 mark for correct final answer with unit.
• Explanation: First, subtract the eggs sold to the supermarket: 6000 - 2450 = 3550. Then, subtract the eggs sold to the restaurant: 3550 - 1890 = 1660. Then, add the newly collected eggs: 1660 + 1500 = 3160.
• Common mistake: Adding the sold eggs instead of subtracting.

20. After first station: 850 - 230 + 180 = 800. After second station: 800 - 150 + 210 = 860.

• Marks: 1 mark for each correct step, 1 mark for correct final answer with unit.
• Explanation: At the first station, subtract those who alighted and add those who boarded: 850 - 230 = 620, then 620 + 180 = 800. At the second station, subtract those who alighted and add those who boarded: 800 - 150 = 650, then 650 + 210 = 860.
• Common mistake: Adding those who alighted instead of subtracting.

End of Answer Key