Question

the inner diameter of a cylindrical pit is 2.1 metre and its depth is 5 metre. find the cost of plastering the inner surface area at the rate of rupees 20 per metre square.
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Answer 1

Diameter of cylindrical pit = 2.1 m

Radius of cylindrical pit = 1.05 m

Depth of Pit = 5 m.

Curved Surface Area = 2πrh

                                   = 2 * 22/7 * 1.05 * 5

                                  = 33 m²

Cost of plastering 1 m² = 20

Cost of plastering 33 m² = 20 * 33

                                         = 660

Therefore, the cost of plastering is 660.

Hope it help!

Answer 2

Answer:

Rs. 660 is the cost of plastering the inner surface area at the rate of rupees 20 per m².

Step-by-step explanation:

$\bold{\underline{\underline{Solution \::}}}$

Given :

• Diameter of inner cylindrical pit = 2.1 m
• Radius = 2.1/2 = 1.05 m
• Height of cylinder = 5 m

According to question,

Inner curved surface area = 2πrh

Substitute the known values in above formula

⇒ $2\:\times\:\dfrac{22}{7}\:\times\:1.05\:\times\:5$

⇒ $6.3\:\times\:1.05\:\times\:5$

⇒ $32.99$

⇒ $\bold{33}$ m² (approx.)

Also, given that cost of plastering per m² is Rs. 20

Then, cost of plastering 33 m³ of area = $33\:\times\: 20$

⇒ Rs. $\bold{660}$