The external and internal diameter of a hollow cylinder are 42 and 28

1.	The external and internal diameter of a hollow cylinder are 42 and 28 cm respectively. Find the cost of painting the cylinder completely at the cost of Rs 0.5/cm2 if the height of cylinder is 5 cm1. Rs 26402. Rs 5503. Rs 19254. Rs 1320
Answer» Correct Answer - Option 4 : Rs 1320 Given- External diameter = 42 cm Internal diameter = 28 cm Cost of painting = Rs 0.5/cm2 Height of cylinder = 5 cm Concept Used- Total Surface Area of a hollow cylinder = 2πh(R + r) + 2π(R² - r²) [where R = External Radius, r = Internal Radius] Calculation- External Radius(R) = 42/2 ⇒ 21 cm Internal Radius(r) = 28/2 ⇒ 14 Total Surface area = 2π × 5 × (21 + 14) + 2π(21² - 14²) ⇒ 44/7 × 5 × 35 + 44/7 × (245) ⇒ 1100 + 1540 ⇒ 2640 cm² ∴ Total cost of painting the cylinder = 2640 × 0.5 ⇒ Rs 1320

The external and internal diameter of a hollow cylinder are 42 and 28 cm respectively. Find the cost of painting the cylinder completely at the cost of Rs 0.5/cm2 if the height of cylinder is 5 cm1. Rs 26402. Rs 5503. Rs 19254. Rs 1320

Answer» Correct Answer - Option 4 : Rs 1320

Given-

External diameter = 42 cm

Internal diameter = 28 cm

Cost of painting = Rs 0.5/cm2

Height of cylinder = 5 cm

Concept Used-

Total Surface Area of a hollow cylinder = 2πh(R + r) + 2π(R² - r²) [where R = External Radius, r = Internal Radius]

Calculation-

External Radius(R) = 42/2

⇒ 21 cm

Internal Radius(r) = 28/2

⇒ 14

Total Surface area = 2π × 5 × (21 + 14) + 2π(21² - 14²)

⇒ 44/7 × 5 × 35 + 44/7 × (245)

⇒ 1100 + 1540

⇒ 2640 cm²

∴ Total cost of painting the cylinder = 2640 × 0.5

⇒ Rs 1320

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