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    Question

    A rectangular piece of copper foil of length 21 cm and

    area 462 cm2 is folded along its width to form a cylinder such that there is only one layer of copper foil on any part of the cylinder. What is the volume (in cm3) of the cylinder so formed?
    A 1886.5 cm³ Correct Answer Incorrect Answer
    B 4312 cm³ Correct Answer Incorrect Answer
    C 808.5 cm³ Correct Answer Incorrect Answer
    D 539 cm³ Correct Answer Incorrect Answer
    E 2425.5 cm³ Correct Answer Incorrect Answer

    Solution

    Width of the rectangular piece of copper foil = 462/21 = 22 cm Since the foil is folded along its width to form a cylinder without any double layer, circumference of the cylinder formed = width of the rectangular foil Also, height of the cylinder so formed = length of the rectangular copper foil So, 2 × π × radius = 22 Radius of cylinder = 22 ÷ (2 × 22/7) = (22/44) × 7 = 3.5 cm So, volume of the cylinder so formed = π × (radius)2 × height = (22/7) × 3.5 × 3.5 × 21 = 808.5 cm³

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