Question

"Question 8 A bus stop is barricaded from the remaining part of the road, by using 50 hollow cones made of recycled cardboard. 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 m^2 , what will be the cost of painting all these cones? (Use π = 3.14 and take= 1.02).

Class 9 - Math - Surface Areas and Volumes Page 221"

Answer 1

Radius of the cone (r) = 40/2 cm = 20 cm = 0.2 m
Height of the cone (h) = 1 m
Let l  be the slant height of a cone.
∴ l = √h2 + r2 
⇒ l = √12 + 0.22 
⇒ l = √1.04 
⇒ l = 1.02 m
Rate of painting = ₹12 per m2 

Curved surface of 1 cone = πrl m2
                                         = (3.14 × 0.2 × 1.02) m2
                                         = 0.64056 m2
Curved surface of such 50 cones = (50 × 0.64056) m2
                                                                 = 32.028 m2
Cost of painting all these cones = ₹(32.028 × 12)
                                                   = ₹384.34

Answer 2

See the attachment....

Hope it help⛎⛎⛎