Question

A bus stop is barricaded from the remaining part of the road, by using 50 hollow cones made of recycled cardboard . each one has a base diameter of 40cm and hieght 1 metre . if the outer side of each of the conesis to be  painted and the cost of painting is Rs 12 m2, what will be the cost of painting all these cones ? (use pie= 3.14 and take root1.4 = 1.02)

Answer 1

so curved surface area of cone is πrl  where r = radius l = lateral height

$l=\sqrt{r^2+h^2}$

h = height 
so l = 100√5 cm
so curved ara = 3.14 x 40 x 100√5 = 12560√5 cm² = 12.56√5 m²
so total area = 12.56√5 x 50 = 628√5 m²

total cost = 12 x 628√5 = Rs. 13053