Question

The inner diameter of a cylindrical pit is 56cm and it is 240 cm deep. Find : (i) its inner curved surface area (ii) its total inner surface area (iii) the cost of plastering the inner surface area at the rate of Rs. 43 per square metre.

Answer 1

I have assumed that the pit is covered from both the upper and lower side.... And then I have calculated the answer...
If any errors... Please write in comments section as soon as possible so that I can correct it...

r=28cm
h=240cm

Inner Curved Surface area= 2*22/7*r*h==2*22/7*28*240==42240cm^2

Total Curved Surface area=
2*22/7*r(h+r)==2*22/7*28* (28+240)==47168cm^2

1m^2 costs ₹43
So by unitary method
(47168/10000)m^2 will cost ₹(43*47168/10000)==₹202.82

NOTE: Convert the cm^2 to m^2 before using it calculate the cost by unitary method.

Answer 2

click the image and see it it is so easy by using the formulae of cylinder