Question

Find the cost of polishing a right circular cylinder at the rate of ₹2.50 per sq cm whose diameter is 8.4cm and height is 20cm .​

Answer 1

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Diameter = 8.4cm

Radius = D/2 = 8.4/2 = 4.2cm

Height = 20cm

C.S.A. of cylinder :-

$= 2\pi \: rh$

$= 2 \times \frac{22}{ \cancel {7} } \times { \cancel{4.2}} \times 20$

$= 2 \times 22 \times 0.6 \times 20$

$= {528cm}^{2}$

Now, Cost of polishing 1cm² = ₹ 2.50

Cost of polishing 528cm² = ₹ 2.50 * 528

$\sf{\purple{\underline{\red{\boxed{\orange{Cost\:=\:₹ 1,320}}}}}}$

Answer 2

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Diameter = 8.4cm

Radius = D/2 = 8.4/2 = 4.2cm

Height = 20cm

C.S.A. of cylinder :-

=2πrh

= 22/7× 4.2 ×20

20 =2×22×0.6×20

= 528cm²

Now, Cost of polishing 1cm² = ₹ 2.50

Cost of polishing 528cm² = ₹ 2.50×528

=> 1,320 Ans.