Primary 2 Mathematics Length Quiz

Primary 2 Mathematics Quiz - Length: Answer Key

Section A: Choose the correct answer. (1 mark each)

1. Answer: (B) metre (m)

Explanation: A classroom is a large space. We use metres to measure longer lengths like rooms, while centimetres are used for shorter objects like pencils. Grams measure mass and litres measure volume.

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2. Answer: (C) 12 cm

Explanation: When measuring with a ruler, always check where the object starts and where it ends. The pencil starts at the 0 cm mark and ends at the 12 cm mark. So the length is 12 − 0 = 12 cm.

Common mistake: Students sometimes count the marks rather than the spaces, or misread where the endpoint lines up.

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3. Answer: (C) 200 cm

Explanation: There are 100 centimetres in 1 metre. To convert metres to centimetres, multiply by 100.

• 2 m = 2 × 100 cm = 200 cm

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4. Answer: (A) 1 m 50 cm and (B) 150 cm (both equal)

Wait — checking again: 1 m 50 cm = 150 cm, and 150 cm = 150 cm. These are the same length! However, if only one answer is allowed, (A) or (B) both represent 150 cm, making this a tie.

Re-evaluating: The question asks which is the longest. If (A) and (B) are equal and both 150 cm, then:

• (C) 1 m 5 cm = 105 cm
• (D) 15 cm

So the longest is 150 cm, which is both (A) and (B). If this is a single-choice question, the intended answer is likely (B) 150 cm as the clearest representation.

Teaching note: Use this to discuss that 1 m 50 cm = 150 cm. The same length can be written in different ways.

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5. Answer: (A) 7 cm

Explanation: To find how much longer, subtract the shorter length from the longer length.

• 45 cm − 38 cm = 7 cm

Common mistake: Some students add instead of subtract. The word "longer" tells us to find the difference, which means subtraction.

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Section B: Fill in the blanks. (1 mark each)

6. Answer: 100

Explanation: The metre (m) and centimetre (cm) are related by a fixed conversion: 1 m = 100 cm. This is like 1 dollar = 100 cents.

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7. Answer: 20

Explanation: A Maths textbook is about the length of a large ruler. 2 cm would be very small (like an eraser), and 200 cm = 2 m would be too big (taller than most Primary 2 students!). About 20 cm is reasonable.

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8. Answer: 325

Explanation: To convert mixed units to cm only:

• 3 m = 3 × 100 cm = 300 cm
• Plus 25 cm = 325 cm

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9. Answer: 78 cm, 85 cm, 1 m, 1 m 10 cm

Explanation: First convert all to the same unit (cm):

• 85 cm = 85 cm
• 1 m = 100 cm
• 78 cm = 78 cm
• 1 m 10 cm = 110 cm

Then order from smallest: 78 cm, 85 cm, 100 cm, 110 cm

Written with original units: 78 cm, 85 cm, 1 m, 1 m 10 cm

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10. Answer: 4 m 50 cm

Explanation: To convert cm to mixed units:

• 450 cm = 400 cm + 50 cm
• 400 cm = 4 m
• So 4 m 50 cm

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Section C: Show your working. (2 marks each)

11. Answer: 2 m 70 cm

Working:

• Start: 5 m = 5 m 0 cm (or 500 cm)
• Cut off: 2 m 30 cm = 230 cm
• Left: 500 cm − 230 cm = 270 cm
• 270 cm = 2 m 70 cm

Or working in metres and centimetres:

• 5 m 0 cm − 2 m 30 cm
• Since 0 cm < 30 cm, borrow 1 m = 100 cm
• = 4 m 100 cm − 2 m 30 cm = 2 m 70 cm

Marking: 1 mark for correct method, 1 mark for correct answer with units

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12. Answer: 70 cm

Working:

• Total = 25 cm + 30 cm + 15 cm
• 25 + 30 = 55
• 55 + 15 = 70 cm

Or: (25 + 15) + 30 = 40 + 30 = 70 cm

Marking: 1 mark for correct addition, 1 mark for correct answer with unit

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13. Answer: 60 cm

Working:

• First convert: 2 m 40 cm = 240 cm
• Divide by 4: 240 cm ÷ 4 = 60 cm

Or check: 60 cm × 4 = 240 cm = 2 m 40 cm ✓

Marking: 1 mark for converting to cm or correct method, 1 mark for correct answer

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14. Answer: 425 m

Working:

• Total distance = 150 m + 275 m
• 150 + 275 = 425 m

Marking: 1 mark for correct addition setup, 1 mark for correct answer with unit

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15. Answer: 5 posts

Working:

• A fence 8 m long with posts every 2 m
• Number of intervals = 8 ÷ 2 = 4 intervals
• Number of posts = intervals + 1 = 4 + 1 = 5 posts

Visual check: Posts at positions 0 m, 2 m, 4 m, 6 m, 8 m = 5 posts.

Common mistake: Students might answer 4, forgetting the post at the start. The "fencepost problem" requires adding 1 when counting items spaced along a length with items at both ends.

Marking: 1 mark for correct method (showing understanding of intervals), 1 mark for correct answer

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Section D: Word problems and reasoning. (2 marks each)

16. (a) Answer: 200 cm

Working:

• 1 m 25 cm = 125 cm
• Total = 125 cm + 75 cm = 200 cm

Or: 1 m 25 cm + 75 cm = 1 m 100 cm = 2 m = 200 cm

Marking: 1 mark for correct conversion/addition method, 1 mark for correct answer

(b) Answer: 100 cm

Working:

• 3 m = 300 cm
• Third piece = 300 cm − 200 cm = 100 cm

Or: 3 m − 2 m = 1 m leftover, but wait — 200 cm = 2 m, and total is 3 m, so third piece is 1 m = 100 cm

Marking: 1 mark for correct subtraction method, 1 mark for correct answer

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17. (a) Answer: Ali

Working:

• Ali: 1 m 20 cm = 120 cm
• Ben: 115 cm
• Cindy: 1 m 8 cm = 108 cm

Comparing: 120 cm > 115 cm > 108 cm, so Ali is the tallest.

Marking: 1 mark for correct conversion/comparison method, 1 mark for correct name

(b) Answer: 12 cm

Working:

• Ali: 120 cm
• Cindy: 108 cm
• Difference: 120 − 108 = 12 cm

Marking: 1 mark for correct subtraction, 1 mark for correct answer with unit

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18. (a) Answer: 200 cm

Working:

• Perimeter = distance all around = length + breadth + length + breadth
• = 60 cm + 40 cm + 60 cm + 40 cm
• = (60 + 60) + (40 + 40)
• = 120 + 80 = 200 cm

Or: 2 × (60 + 40) = 2 × 100 = 200 cm

Teaching note: "Perimeter" means the total distance around a shape. For a rectangle, opposite sides are equal.

Marking: 1 mark for correct method (adding all sides or formula), 1 mark for correct answer with unit

(b) Answer: 20 cm

Working:

• Difference = 60 cm − 40 cm = 20 cm

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19. (a) Answer: 7 m

Working:

• Length = 2 m, Breadth = 1 m 50 cm
• Perimeter = 2 m + 1 m 50 cm + 2 m + 1 m 50 cm
• = 4 m + 3 m = 7 m

Or convert: 2 m + 1.5 m + 2 m + 1.5 m = 7 m

Teaching note: "Border" goes all around the edge, so we need the perimeter.

Marking: 1 mark for correct perimeter method, 1 mark for correct answer with unit

(b) Answer: $35

Working:

• Cost = 7 m × $5/m = **$35**

Marking: 1 mark for correct multiplication, 1 mark for correct answer with dollar sign

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20. (a) Answer: 140 m

Working:

• Path A→B→C = 60 m + 80 m = 140 m

Marking: 1 mark for correct addition, 1 mark for correct answer with unit

(b) Answer: 90 m

Working:

• Shortcut distance = total path − saving
• = 140 m − 50 m = 90 m

Or: If the shortcut saves 50 m, then shortcut = 140 − 50 = 90 m

Teaching note: The direct path is shorter than going around the corner. The "saving" is the difference between the two routes.

Marking: 1 mark for correct subtraction method, 1 mark for correct answer with unit

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Marking Summary

Section	Questions	Marks
A	1–5	5
B	6–10	5
C	11–15	10
D	16–20	10
Total	1–20	30

Wait — correction: Rechecking marks allocation.

Actually: Section A (5 × 1 = 5), Section B (5 × 1 = 5), Section C (5 × 2 = 10), Section D (5 × 2 = 10, but Q16 and Q17 and Q18, Q19, Q20 each have parts).

Rechecking: Q16 (2 marks), Q17 (2 marks), Q18 (2 marks), Q19 (2 marks), Q20 (2 marks) = 10 marks.

Total: 5 + 5 + 10 + 10 = 30 marks

But quiz header says Total Marks: 20.

Correction needed: The quiz as written has 30 marks. However, the header states 20. For consistency with the header, actual marks are over 20 if Sections C and D are 1 mark each, or the header is wrong.

Given standard Primary 2: Adjusting interpretation — Sections A and B are 1 mark each (10 marks), Sections C and D are 1 mark working + 1 mark answer = 2 marks each, total 20 marks.

The header Total Marks: 20 is correct for:

• Section A: 5 × 1 = 5 marks (but only 5 questions... that's 5 marks)
• Actually: 5 + 5 + 10 = 20 if C is 5 questions × 2 = 10, and D is...

Let me recalculate properly from the document:

• A: 5 questions × 1 = 5
• B: 5 questions × 1 = 5
• C: 5 questions × 2 = 10
• D: 5 questions × 2 = 10

Total = 30 marks.

The header should say 30 marks or questions need mark adjustment. Since the instructions say "execute based on what I wrote," the document has an inconsistency.

Corrected interpretation: The quiz as rendered awards 2 marks each for Q11-Q20 (10 questions × 2 = 20 marks) plus 10 marks for A and B = 30 total. The original header of 20 was based on an earlier draft.

For this answer key, marks are awarded as labeled in sections: Total = 30 marks.

However, to match header: If we strictly need 20 marks, then C and D would be 5 marks total (1 each). Given the complexity, 2 marks each is appropriate for Primary 2 problem solving.

Final note: The quiz contains 20 top-level questions as required. Subparts (a), (b) share the 2 marks per top-level question.

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End of Answer Key