Primary 4 Mathematics · Chapter 12 · Answers and explanations
Lesson 12.3: Finding Unknown Sides of Rectangles (answers)
Section A · Multiple choice 4 marks
1. A rectangle has an area of 72 cm² and a length of 9 cm. What is its breadth?1 mark
(A) 8 cm(B) 63 cm(C) 81 cm(D) 4 cm
Answer: (A) 8 cmBreadth = 72 ÷ 9 = 8 cm.
2. A rectangle has a perimeter of 40 cm and a length of 12 cm. What is its breadth?1 mark
(A) 28 cm(B) 8 cm(C) 16 cm(D) 4 cm
Answer: (B) 8 cmLength + breadth = 40 ÷ 2 = 20 cm. Breadth = 20 − 12 = 8 cm.
3. A rectangle has a breadth of 5 m and an area of 85 m². What is its length?1 mark
(A) 80 m(B) 425 m(C) 17 m(D) 12 m
Answer: (C) 17 mLength = 85 ÷ 5 = 17 m.
4. The length of a rectangle is twice its breadth. Its perimeter is 54 m. What is its breadth?1 mark
(A) 18 m(B) 27 m(C) 6 m(D) 9 m
Answer: (D) 9 mLength + breadth = 27 m, which is 3 units. 1 unit = 27 ÷ 3 = 9 m. The breadth is 9 m.
Section B · Write your answer 11 marks
5. A rectangle has an area of 91 m² and a length of 13 m. What is its breadth?1 mark
Answer: 7 m91 ÷ 13 = 7 m.
6. A rectangle has a perimeter of 62 cm and a breadth of 11 cm. What is its length?1 mark
Answer: 20 cmLength + breadth = 62 ÷ 2 = 31 cm. Length = 31 − 11 = 20 cm.
7. A rectangle has an area of 150 cm² and a breadth of 6 cm. What is its length?1 mark
Answer: 25 cm150 ÷ 6 = 25 cm.
8. A rectangle has a perimeter of 46 cm and a length of 15 cm. What is its breadth?1 mark
Answer: 8 cmLength + breadth = 23 cm. Breadth = 23 − 15 = 8 cm.
9. What is the area of a rectangle 16 cm long and 7 cm wide?1 mark
Answer: 112 cm²16 × 7 = 112 cm².
10. The length of a rectangle is 3 times its breadth. Its perimeter is 48 cm. Find its area.2 marks
Answer: 108 cm²Length + breadth = 24 cm = 4 units. 1 unit = 6 cm, so breadth = 6 cm and length = 18 cm. Area = 18 × 6 = 108 cm².
11. A rectangular room has an area of 108 m² and a breadth of 9 m. What is its perimeter?2 marks
Answer: 42 mLength = 108 ÷ 9 = 12 m. Perimeter = 12 + 9 + 12 + 9 = 42 m.
12. A rectangular poster has a length of 40 cm and a perimeter of 130 cm. Find its area.2 marks
Answer: 1000 cm²Length + breadth = 65 cm. Breadth = 65 − 40 = 25 cm. Area = 40 × 25 = 1000 cm².
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