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Question:

A bus stop is barricaded from the remaining part of the road by using 50 hollow cones made of recycled cardboards. Each cone has a base diameter of 40 cm and height 1 m. If the outer side of each of the cones is to be painted and the cost of painting is 12 per m², what will be the cost of painting all these cones?

Solution:

Given, diameter=40 cm
Radius,r=40/2cm=20 cm=0.2 m
Height,h=1 m
Slant height,l=√h²+r²=√1²+0.2² m=√1.04 m=1.02 m
CSA=πrl=(3.14×0.2×1.02) m²=0.64056 m²
CSA of 50 cones=50×0.64056 m²=32.028 m²
Cost of painting 1m² area=Rs.12
Cost of painting 32.028 m² area=Rs.32.028×12=Rs.384.336≈Rs.384.34