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    Question

    A hollow cylinder has an external radius of 7 cm and an

    internal radius of 5 cm. If the height of the cylinder is 10 cm and it is melted to form a sphere, find the radius of the sphere.(Approx)
    A 4.75 Correct Answer Incorrect Answer
    B 6.25 Correct Answer Incorrect Answer
    C 5.65 Correct Answer Incorrect Answer
    D 4.85 Correct Answer Incorrect Answer

    Solution

      Volume of the hollow cylinder- Volume of cylinder = π (R2 - r²) h = π × 10 × (72 -52) = π × 10 × (49-25) = π × 10 × 24 = 240 π cm³   Volume of the sphere: Volume of sphere =4/3 πr3 Equating volumes- 240π = 4/3 πr3 240 = 4/3 r3 r3 =180 r = √180 r = 5.65 cm(approx.)

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