Question

a cylindrical well in 21 m deep with outer and inner diameter are 21 m and 14 m respectively find the cost of renovating the inner curved surface and Outer curved surface @ rupees 25 per square metre

Answer 1

$inner \: radius \: r1 = \frac{14}{2} = 7 \\ outer \: radius \: r2 = \frac{21}{2} = 10.5 \\ height \: \: h = 21 \\ sum \: of \: inner \: \: and \: \: outer \: \: curved \\ surface \: \: area = 2\pi(r1 + r2)h \\ = 2 \times \frac{22}{7} \times (7 + 10.5) \times 21 \\ = 2310 \: {cm}^{2} \\ therefore \: \: cost \: \: of \: \: renovation \\ = 2310 \times 25 = 57750$