Question

a well has to be dug out that is to be 22.5m deep and of diameter 7m. The cost of plastering the inner curved surface at Rs. 30 per square meter is:

Answer 1

given: h      =22.5m
         diameter=7m
hence, r=3.5m

we know that CSA of a cylinder is 2.pi.r.h
hence, CSA of the inner curved surface= 2.22/7.3.5.22.5
                                                        =  465m²
therefore cost of plastering = 14850₹

Answer 2

given:- 
h= 22.5
d=7m
r=3.5m
CSA of a cylinder is =2 \pi/r
CSA of the inner curved surface= 2.22/7.3.5.22.5
=465 m^{2} 

therefore cost of plastering=14850