Question
Download Solution PDFThe cost of painting a solid cone at 30 paise per cm2 is ₹1056. Find the radius of the cone if its slant height is 36 cm. \(\left(Use \,\,\pi=\frac{22}{7}\right)\)
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFGiven
Cost of painting: ₹1056
Cost per cm2 of painting: ₹0.30
Slant height (l) of the cone: 36 cm
Concept Used:
Total Surface Area of a Cone = πr(r + l)
Solution:
Total area painted = Total cost / Cost per cm2 = 1056 / 0.30 = 3520 cm2
Total surface area of cone = πr(r + l)
⇒ πr(r + l) = 3520
⇒ 22/7 × r (r + l) = 3520
⇒ r2 + 36r - 1120 = 0
⇒ r2 + 56r - 20r - 1120 = 0
⇒ (r + 56)(r - 20) = 0
⇒ r = 20 cm
Therefore, the radius of the cone is 20 cm.
Last updated on Jul 8, 2025
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