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If the ratio between the curved surface area of two cones is 5 ∶ 39 and the ratio between their radius is 1 ∶ 3. Find the ratio between their slant height.1. 7 ∶ 122. 5 ∶ 133. 13 ∶ 54. 12 ∶ 13 |
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Answer» Correct Answer - Option 2 : 5 ∶ 13 Given: Ratio between CSA = 5 ∶ 39 Ratio between diameters = 1 ∶ 3 Formula used: CSA of cone = πrl, where l is slant height and r is the radius of the base. Calculation: Let the l1 and l2 be the slant height of two cones. Curved surface area of cone 1, CSA1 = πR1l1 Curved surface area of cone 2, CSA2 = πR2l2 According to the question, CSA1/CSA2 = 5/39 ⇒ (πR1l1)/( πR2l2) = 5/39 ⇒ R1/R2 × l1/l2 = 5/39 ⇒ 1/3 × l1/l2 = 5/39 ⇒ l1/l2 = 5/13 ∴ The ratio between their slant height is 5 ∶ 13. |
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