Question

the inner diameter of a well is 4.2 0 m and its depth is 10metre. find the inner surface area of the well. find cost of plastering it from inside at the rate Rs52 per square metre

Answer 1

h = 10 m
d = 4.2 m so r = 2.1 m
CSA = ?
CSA of cylinder = 2πrh
= 2 * 22/7 * 2.1 * 10
= (44*3) = 132 m²
total cost = rate * area
= 132 * 52
= ₹6874

Answer 2

d = 4.2 , so r=2.1 =21/10
$inner \: csa = \frac{2 \times 22 \times 21 \times 10}{7 \times 10} \\ = 22 \times 6 = 132 {m}^{2} \\ cost \: = rs \: 132 \times 52$