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A hole cylinder iron pipe as of length 40cm its internal and external radii are 4cm and 12 cm it is melted and recasted into solid cylinder and length 20

cm find the radius of new solid


Volume of cylinder=πh(R²-r²)
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Volume of hollow cylinder = πh(r1²-r2²)
= π * 40 * (12²-4²)
= π * 40 *128
=5120π cm³

Volume of solid cylinder = π r² h = volume of hollow cylinder
π r² 20 = 5120 π
r² = 5120/20
r² = 256
r = √256
r = 16 cm
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