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Question
A frustum of a cone is 9 cm thick and the diameters of its circular ends are 28 cm and 4 cm. Find the volume and lateral surface area of the frustum.
(Take π = 22/7).
Solution
Volume
`=(pih)/3 (R^2 + Rr + r^2)`
`=9 xx pi /3 ((28/2)^2 + (4/2)^2 + 28/2 xx 4/2)`
`=3pi((14)^2 + 4+14 xx 2)`
`=684 pi cm^3`
S.A. = `pi(14+2)sqrt((14 - 2)^2) + 9 = 240 pi cm^2`
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