students of class XII presented a gift to their school in the form of an electrical lamp in tje shape of a glass hemisphercal base surmounted by a mettallic cylindrical top of same radius 21cm and height 3.5cm. The top was silver coated and the glass surface was painted red. (1)what is the cost of silver coating the top at the rate of ₹5per 100cm square.? (2) what is the surface area of glass to be painted red?
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(1) Cost of silver coating is Rs 23.10
(2) Surface area of glass to be painted red is 882П cm²
It is given that the radius of the cylinder (r) is 21cm
Again, the height is (h) = 3.5cm
We know that the curved surface of the cylinder of radius r and height h is = 2Пrh
Substituting the values, we get
CSA = 2П*21*3.5 cm²
= 147П cm²
Putting П = 22/7, we get
CSA = 462 cm².
Given that, per 100 cm² costs Rs 5.
So, 1 cm² would cost = Rs (5/100)
Thus, 462 cm² would cost = Rs (462*5/100) = Rs 23.10
Radius of hemisphere = 21cm
Surface area = 2Пr²
Replacing r as 21cm, we get
SA = 2П(21)²
= 882П cm²
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