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    IBHardGeometry & Trigonometry7–9

    Paint for a Silo of Cylinder and Cone

    Tinta para um Silo de Cilindro e Cone

    A grain silo is a cylinder of radius 22 m and height 55 m, topped by a cone of height 1.51.5 m with the same radius. Only the curved outside surfaces are painted — not the base, and not the join. One litre of paint covers 6 m26 \text{ m}^{2} and paint is sold in whole litres. How many litres are needed?

    The cone's curved surface needs its slant, which the given height is not. Treat the two surfaces separately, and remember at the end that a shop sells whole tins.

    Solution

    Step 1 of 11

    1. 1.Slant height of the cone, by Pythagoras: