Primary 1 Mathematics Addition Subtraction Quiz

Primary 1 Mathematics Quiz - Addition Subtraction — Answer Key

Total Marks: 30
Topic: Addition and Subtraction (within 100, no renaming)

Note for marker: All addition and subtraction questions in this quiz are designed to be solved without regrouping across tens (e.g., 34 + 25 is fine because 4 + 5 = 9 with no carry, and 7 + 8 in Q18 is a valid ones-digit sum without borrowing). Each question's working is shown below.

Section A — Mental Addition Within 20 (Questions 1–5) [5 marks]

1. 7 + 3 = 10

• Concept: "Adding on" combines two sets; 7 and 3 together make a friendly ten.
• Method: Count on from 7: 8, 9, 10. (1 mark)

2. 6 + 5 = 11

• Concept: Reinforces that 6 + 5 crosses a ten, building a known fact.
• Method: 6 + 4 = 10, then + 1 more = 11. (1 mark)

3. 9 + 4 = 13

• Concept: Doubles-plus-one style: 9 is close to 10.
• Method: 9 + 1 = 10, then 10 + 3 = 13. (1 mark)

4. 8 + 8 = 16

• Concept: Doubles (8 + 8) fact; useful anchor for later sums.
• Method: Double 8 = 16. (1 mark)

5. 2 + 7 + 5 = 14

• Concept: Adding more than two single-digit numbers; commutative property — reorder to make a ten.
• Method: 2 + 7 + 5 = (7 + 3) + (2 + 2) = 10 + 4 = 14. (1 mark)
• Common mistake: Counting all from 1 each time instead of "adding on."

Section B — Mental Subtraction Within 20 (Questions 6–10) [5 marks]

6. 10 − 4 = 6

• Concept: "Taking away" from a ten.
• Method: Count back 4 from 10: 9, 8, 7, 6. (1 mark)

7. 13 − 5 = 8

• Concept: Counting back, or using the inverse: 8 + 5 = 13.
• Method: 13 − 3 = 10, then 10 − 2 = 8. (1 mark)

8. 15 − 7 = 8

• Concept: Subtraction crosses a ten.
• Method: 15 − 5 = 10, then 10 − 2 = 8. (1 mark)

9. 11 − 6 = 5

• Concept: Inverse relationship with addition: 5 + 6 = 11.
• Method: Count back 6 from 11: 10, 9, 8, 7, 6, 5. (1 mark)

10. 18 − 9 = 9

• Concept: Half of 18; reinforces the 18 = 9 + 9 doubles fact.
• Method: 18 − 8 = 10, then 10 − 1 = 9. (1 mark)

Section C — Addition Within 100 (No Renaming) (Questions 11–15) [8 marks]

11. 24 + 5 = 29

• Concept: Adding a 1-digit number to a 2-digit number (ones only).
• Method: Ones: 4 + 5 = 9; Tens stay 2 → 29. (1 mark)

12. 36 + 20 = 56

• Concept: Adding tens to a 2-digit number; ones digit is unchanged.
• Method: 3 + 2 = 5 tens; ones digit remains 6 → 56. (1 mark)

13. 41 + 32 = 73

• Concept: Adding two 2-digit numbers without renaming.
• Method: Ones: 1 + 2 = 3; Tens: 4 + 3 = 7 → 73. (1 mark)
• Check: No regrouping is needed because 1 + 2 = 3 (less than 10) and 4 + 3 = 7 (less than 10).

14. Mei Ling: 25 + 14 = 39 stickers.

• Concept: Word problem — "altogether" means add.
• Method:
  • Number sentence: 25 + 14 = 39 (1 mark)
  • Final answer: 39 stickers (1 mark)
• Teaching note: Encourage students to underline key words like "altogether" and "more" to choose the operation.

15. Picture question — Jar A (34) + Jar B (25) = 59 marbles.

• Visual required: Two jars labelled "Jar A" (34 marbles) and "Jar B" (25 marbles).
• Method: 34 + 25 → Ones: 4 + 5 = 9; Tens: 3 + 2 = 5 → 59 marbles. (2 marks)
• Common mistake: Reading "thirty-four" as "thirteen" — emphasise the "ty" in tens (3 tens, 4 ones).

Section D — Subtraction Within 100 (No Renaming) (Questions 16–20) [12 marks]

16. 58 − 3 = 55

• Concept: Subtracting a 1-digit number from a 2-digit number (ones only).
• Method: Ones: 8 − 3 = 5; Tens stay 5 → 55. (1 mark)

17. 67 − 40 = 27

• Concept: Subtracting tens from a 2-digit number; ones digit is unchanged.
• Method: 6 − 4 = 2 tens; ones stay 7 → 27. (1 mark)

18. 89 − 25 = 64

• Concept: Subtracting two 2-digit numbers without renaming.
• Method: Ones: 9 − 5 = 4; Tens: 8 − 2 = 6 → 64. (1 mark)
• Check: 9 − 5 = 4 (no borrowing needed because 9 ≥ 5); 8 − 2 = 6 (no borrowing needed).

19. Bala: 63 − 21 = 42 stamps.

• Concept: Word problem — "left" and "gives away" mean subtract.
• Method:
  • Number sentence: 63 − 21 = 42 (1 mark)
  • Final answer: 42 stamps (1 mark)
• Teaching note: Have students retell the problem in their own words: "Bala started with 63 stamps, gave 21 away, so 42 remain."

20. Oranges: 75 − 43 = 32 oranges.

• Concept: Real-life context — "left" means subtract.
• Method:
  • Number sentence: 75 − 43 = 32 (1 mark)
  • Final answer: 32 oranges (1 mark)
• Step-by-step:
  • Ones: 5 − 3 = 2.
  • Tens: 7 − 4 = 3.
  • Combine: 32.
• Common mistake: Subtracting 43 from 75 as "75 − 40 − 3" but losing the ones place; or writing 75 − 43 as 32 by mistake as 22. Encourage lining up the place values.

Mark Allocation Summary