Primary 3 Mathematics Semestral Assessment 2 (End of Year) Paper 1

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SA2 Practice Paper - Mathematics Primary 3

Version 1 of 5 - ANSWER KEY

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SECTION A: Multiple-Choice Questions (20 marks)

1. [2 marks] 3

Teaching note: In the number 7 358, we read the digits from left to right by place value: 7 is thousands, 3 is hundreds, 5 is tens, 8 is ones. The digit in the hundreds place is 3. Common mistake: Confusing "hundreds place" with "value of the hundreds digit" (which would be 300).

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2. [2 marks] 4 000

Teaching note: The digit 4 is in the thousands place in 4 926. Its value is 4 × 1 000 = 4 000. Common mistake: Choosing "4" which is just the digit itself, not its value. The word "value" always means we multiply the digit by its place value.

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3. [2 marks] 6 840

Teaching note: To compare 4-digit numbers, start from the thousands place and move right if needed. All have 6 thousands. In hundreds place: 8 > 4, so 6 840 and 6 804 are larger than the others. Compare these two: both have 8 hundreds, then 4 > 0 in the tens place. So 6 840 is largest.

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4. [2 marks] 3 102, 3 120, 3 201, 3 210

Teaching note: All start with 3 thousands. Compare hundreds: 1 < 2, so 3 102 and 3 120 come before 3 201 and 3 210. Between 3 102 and 3 120: 0 < 2 in tens place. Between 3 201 and 3 210: 0 < 1 in tens place. Ascending order means smallest to largest (going up like stairs).

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5. [2 marks] 5 307

Teaching note: Break down: 5 000 + 300 + 0 tens + 7 ones = 5 307. Check: there are no tens mentioned, so we need 0 in the tens place as a placeholder. Common mistake: Writing 5 37 or 537, forgetting the thousands and the zero placeholder.

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6. [2 marks] 6 945

Teaching note: "100 more than" means add 100. 6 845 + 100 = 6 945. The hundreds digit increases from 8 to 9. Using place value: 6 845 + 100 = 6 000 + 800 + 40 + 5 + 100 = 6 000 + 900 + 40 + 5 = 6 945.

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7. [2 marks] 5 000

Teaching note: To round to the nearest thousand, look at the hundreds digit. In 4 567, the hundreds digit is 5. The rule is: 5 or more, round up; 4 or less, round down. Since 5 ≥ 5, we round 4 thousands up to 5 000. Common mistake: Rounding to 4 000 by looking at the thousands digit rather than the hundreds digit.

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8. [2 marks] 2 500

Teaching note: Find the pattern: 2 300 − 2 100 = 200. So we add 200 each time. 2 300 + 200 = 2 500. Verify: 2 500 + 200 = 2 700 ✓ This is an arithmetic sequence with common difference 200.

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9. [2 marks] 4 544

Teaching note: Use standard subtraction with regrouping:

  8 0 0 0
- 3 4 5 6
-----------
  4 5 4 4

Step 1: 0 − 6 (can't), regroup: 10 − 6 = 4 Step 2: 9 − 5 = 4 (after regrouping) Step 3: 9 − 4 = 5 (after regrouping) Step 4: 7 − 3 = 4 (after regrouping)

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10. [2 marks] 2 000 × 2

Teaching note: Calculate each:

• 3 000 + 2 000 = 5 000
• 5 000 − 500 = 4 500
• 2 000 × 2 = 4 000... wait, let me recheck: 2 000 × 2 = 4 000

Actually: 3 000 + 2 000 = 5 000; 5 000 − 500 = 4 500; 2 000 × 2 = 4 000; 9 000 ÷ 2 = 4 500.

So 3 000 + 2 000 = 5 000 is largest. The correct answer is 3 000 + 2 000.

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SECTION B: Short-Answer and Structured Questions (30 marks)

11. [1 mark] Five thousand six hundred and eight

Teaching note: Write in words with proper place value. 5 thousands, 6 hundreds, 0 tens (say "six hundred"), 8 ones ("and eight"). The word "and" connects hundreds to the tens/ones. In Singapore format, we include "and" before the last two digits.

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12 (a). [1 mark] 9 000

Teaching note: The digit 9 is in the thousands place. Value = 9 × 1 000 = 9 000.

12 (b). [1 mark] 100

Teaching note: The digit 1 is in the hundreds place. Value = 1 × 100 = 100.

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13. [1 mark] 200

Teaching note: 6 250 = 6 000 + ? + 50. Using place value: 6 250 = 6 000 + 200 + 50. The missing value is 200. This represents 2 hundreds.

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14. [2 marks] 4 980, 4 908, 4 890, 4 089

Teaching note: Descending order means largest to smallest (going down).

Step 1: All have 4 thousands except 4 089 (which is smallest). Step 2: Compare 4 980, 4 908, 4 890: all have 9 hundreds. Step 3: Compare tens: 8 > 0, so 4 980 > 4 908? No wait: 4 980 has 8 tens, 4 908 has 0 tens, 4 890 has 9 tens.

Correct order: 4 980 (9 thousands, 8 tens) → actually re-compare:

• 4 980: 9 hundreds, 8 tens
• 4 908: 9 hundreds, 0 tens
• 4 890: 8 hundreds, 9 tens

So 4 980 > 4 908 > 4 890 > 4 089

Marking: [2] fully correct; [1] one number out of place; [0] more errors.

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15. [2 marks] 2 100, 2 700 (one mark each blank)

Teaching note: Pattern: 1 800 − 1 500 = 300. Common difference is 300.

• 1 800 + 300 = 2 100
• 2 400 + 300 = 2 700

Verify: 1 500, 1 800, 2 100, 2 400, 2 700 — each increases by 300 ✓

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16. [2 marks] 6 245

Teaching note: Use standard addition algorithm:

  3 4 5 6
+ 2 7 8 9
-----------
  6 2 4 5

Step by step:

• Ones: 6 + 9 = 15, write 5, carry 1 to tens
• Tens: 5 + 8 + 1 = 14, write 4, carry 1 to hundreds
• Hundreds: 4 + 7 + 1 = 12, write 2, carry 1 to thousands
• Thousands: 3 + 2 + 1 = 6

Final answer: 6 245

Marking: [1] correct method with one calculation error; [2] fully correct.

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17. [2 marks] 2 655

Teaching note: "Subtract 2 345 from 5 000" means 5 000 − 2 345.

  5 0 0 0
- 2 3 4 5
-----------
  2 6 5 5

Step by step with regrouping:

• Ones: 0 − 5, can't, regroup: 10 − 5 = 5
• Tens: 9 − 4 = 5 (after regrouping)
• Hundreds: 9 − 3 = 6 (after regrouping)
• Thousands: 4 − 2 = 2 (after regrouping)

Common mistake: Writing 2 345 − 5 000 = −2 655. Watch the order: "subtract A from B" means B − A.

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18. [2 marks] 4 325 pupils

Teaching note: "Altogether" means addition.

• Boys: 2 450
• Girls: 1 875
• Total: 2 450 + 1 875

Working:

  2 4 5 0
+ 1 8 7 5
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  4 3 2 5

2 450 + 1 875 = 4 325

Marking: [1] correct method with calculation error; [2] fully correct with units.

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19. [3 marks] $551

Teaching note: Two-step problem: find total cost first, then find change.

Step 1: Total cost = $2 599 +$1 850

  2 5 9 9
+ 1 8 5 0
-----------
  4 4 4 9

Total = $4 449

Step 2: Change = $5 000 −$4 449

  5 0 0 0
- 4 4 4 9
-----------
    5 5 1

Change = $551

Marking breakdown:

• [1] correct total cost ($4 449)
• [1] correct method for change with correct subtraction
• [1] correct final answer with $ unit

Common mistake: Forgetting to add total cost first, or subtracting $2 599 from$5 000 only.

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20. Refer to number line showing points A(2 000), B(2 250), C(2 750), D(3 000) with interval 250.

(a) [1 mark] 2 750

Teaching note: Point C is located at 2 750 on the number line, which is 3 major intervals from A (2 000 + 250 + 250 + 250 = 2 750, or 2 000 + 750 = 2 750).

(b) [2 marks] 750

Teaching note: Point B = 2 250, Point D = 3 000. Difference = 3 000 − 2 250 = 750

Working shown:

• Point D: 3 000
• Point B: 2 250
• 3 000 − 2 250 = 750

Or count intervals: from B to D is 3 intervals of 250 = 750.

Marking: [1] identify both values correctly; [1] correct subtraction.

(c) [1 mark] 750

Teaching note: Point A = 2 000, Point C = 2 750. 2 750 − 2 000 = 750. So Point A is 750 less than Point C.

(d) [1 mark] Any number from 2 251 to 2 749 inclusive

Teaching note: "Between" in primary mathematics typically means strictly between (not including the endpoints). Any whole number greater than 2 250 and less than 2 750 is acceptable. Examples: 2 300, 2 500, 2 749. Common mistake: Writing 2 250 or 2 750, which are the endpoints, not between.

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TOTAL MARKS: 50

Section A: 20 marks Section B: 30 marks