A circular park has an area of 3850 square metres. What is the cost of fencing it along its boundary at ₹28 per metre? (Use π = 22/7.)

π$r^2=3850$ gives $r^2=3850\times 7/22=1225$, so $r=35$ m. Fencing runs along the circumference = $2\times (22/7)\times 35=220$ m, and $220\times 28$ = ₹6160. ₹3080 uses π$r=110$ m, dropping the 2 of 2π$r$; ₹12320 fences a circle of radius 70 m, the diameter mistaken for the radius; ₹107800 charges the per-metre rate on the 3850 sq m of area instead of on the boundary length.