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The height of a cone is 21 cm. Find the area of the base if the slant height is 28 cm.
Height of cone (h) = 21 cm
Slant height ( l )=28 cm
∴l2=r2 + h2 =r == =7√7 cm
∴ Area of the base = πr2=×cm2 = 1078 cm2
A bus stop is barricaded from the remaining part of the road, by using 50 hollow cone made of recycled card-board. 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 Rs. 12 per m2. What will be the cost of painting all these cones. (Use π=3.14 and = 1.02).