Question

22
Use z =
7
unless otherwise stated.


A right circular cylinder is closed at both ends. Find the cost of polishing its total surface at
* 0.50 per square cm, if the radius of the cylinder is 7 cm and depth is 12 cm.
3. The diameter of a well is 21 m and it is
2.
1
Td​

Answer 1

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Step-by-step explanation:

Let the radius of the original cylinder =r cm and height =h cm

Surface Area of a Cylinder =2πrh

New radius after decrease =10075r=0.75r

New height after increase =100125h=1.2h5

New surface area of the cylinder =2π×0.75r×1.25h=1.875πrh

Since, 1.875<2, the surface area has decreased. 

%decrease =Original Surface AreaOriginal Surface area - New Surface Area ×100

=2πrh2πrh−1.875πrh×100

=20.125×100=6.25%

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