Difficulty: Easy
Correct Answer: l = 64 cm; b = 16 cm
Explanation:
Introduction / Context: This question tests basic understanding of rectangle geometry and perimeter relations. When a rectangle’s perimeter and the ratio between its length and width are known, the actual dimensions can be found by forming a simple algebraic equation.
Given Data / Assumptions:
Concept / Approach: The perimeter of a rectangle is given by 2*(length + breadth). Substitute the given relationship between length and width into the perimeter formula and solve for the unknown dimension.
Step-by-Step Solution: Perimeter = 2*(l + b) 160 = 2*(4b + b) 160 = 2*5b = 10b b = 16 cm l = 4b = 4*16 = 64 cm
Verification / Alternative check: Substituting l = 64 and b = 16 into the perimeter formula gives 2*(64 + 16) = 2*80 = 160 cm, which matches the given perimeter exactly.
Why Other Options Are Wrong: 48 cm and 24 cm: length is only twice the width, not four times. 65 cm and 16 cm: perimeter exceeds 160 cm. 16 cm and 64 cm: reverses length and width. 40 cm and 20 cm: does not satisfy the four-times condition.
Common Pitfalls: Forgetting to multiply the sum by 2 in the perimeter formula. Mixing up which dimension is four times the other. Arithmetic errors while solving for b.
Final Answer: Length = 64 cm and Width = 16 cm
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