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The radius of the base of a solid cone is 9 cm and its height is 21 cm. It cut into 3 parts by two cuts, which are parallel to its base. The cuts are at height of 7 cm and 14 cm from the base respectively. What is the ratio of curved surface areas of top, middle and bottom parts respectively?1). 1 ∶ 4 ∶ 82). 7 ∶ 23 ∶ 363). 1 ∶ 3 ∶ 94). 1 ∶ 6 ∶ 12 |
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Answer» Height will be divided in 3 parts and heights for three cones will be 7cm, 14cm and 21cm, in the ratio (1 ? 2 ? 3) Also the RADIUS of the three cones will be 3CM, 6cm and 9cm, in the ratio (1 ? 2 ? 3) Since curved surface area of a cone = πrl ⇒ Ratio of curved surface AREAS of three cones = r1l$1 ? r2l$2 ? r3l$3 = 21 : 90 : 198 ∴ Ratio of curved surface areas of top, middle and bottom parts = 21 ? (90 - 21) ? (198 - 90) = 21 ? 69 ? 108 =7 ? 23 ? 36 |
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