12 cylindrical pillars of a building have to be cleaned.If the diameter of each pillar is 42cm and the height of each pillar is 5m, what will be the cost of cleaning these at the rate of Rs.5 per sq.m
Diameter of pillar=42cm
Radius=r=422=21cm=21100m
Curved area of pillar=2πrh=2×227×21100×5=6.6sq.m
Total area of 12 pillars=12×6.6sq.m=79.2sq.m
Cost of cleaning for 1 sq.m=Rs.5
Cost of cleaning for 79.2 sq.m=Rs.5×79.2=Rs.396
∴ Cost of cleaning for 79.2 sq.mRs.396