A well of diameter 4 $m$ is dug 21 $m$ deep. Digging costs ₹25 per $m^3$ and plastering its inner curved surface costs ₹8 per $m^2$. Find the total cost in rupees. Take π = 22/7.

Radius = 2 $m$. Earth dug out = $(22/7)\times 2^2\times 21=264m^3$, costing $264\times 25$ = ₹6600. Inner curved surface = 2πrh = $2\times (22/7)\times 2\times 21=264m^2$, costing $264\times 8$ = ₹2112. Total = 6600 + 2112 = ₹8712. (Answering ₹6600 or ₹2112 pays only one of the two bills; using the diameter 4 $m$ as the radius quadruples the digging to ₹26400.)