The inner and outer radii of a hemispherical wooden bowl are 6 cm and 8 cm, respectively. Its entire surface has to be polished and the cost of polishing π cm2 is Rs. 50. How much will it cost to polish the bowl?

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SSC CHSL Exam 2024 Tier-I Official Paper (Held On: 08 Jul, 2024 Shift 4)
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  1. Rs. 11,400
  2. Rs. 10,000
  3. Rs. 12,000
  4. Rs. 11,600

Answer (Detailed Solution Below)

Option 1 : Rs. 11,400
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SSC CHSL Exam 2023 Tier-I Official Paper (Held On: 02 Aug 2023 Shift 1)
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100 Questions 200 Marks 60 Mins

Detailed Solution

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Given:

Inner radius (r1) = 6 cm

Outer radius (r2) = 8 cm

Cost to polish π cm2 = ₹50

Formula used:

Surface area of hemispherical bowl = Outer curved surface area + Inner curved surface area + Area of circular rim

Outer curved surface area = 2πr22

Inner curved surface area = 2πr12

Area of circular rim = π(r22 - r12)

Total surface area = 2πr22 + 2πr12 + π(r22 - r12)

Calculation:

Total surface area = 2π(8)2 + 2π(6)2 + π[(8)2 - (6)2]

⇒ Total surface area = 2π(64) + 2π(36) + π(64 - 36)

⇒ Total surface area = 128π + 72π + 28π

⇒ Total surface area = 228π cm2

Cost per π cm2 = ₹50

Cost = 228 × ₹50

⇒ Cost = ₹11,400

∴ The cost to polish the bowl is ₹11,400.

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