Question

solve it fast please

Class 9 EXERCISE 13.3
Q no. 8
NCERT book

Answer 1

Sol.

Let r  be the radius , h  be the height and l  be the slant height of a cone. Then ,
r=(402)cm = 20 cm = .2 m, 
and h = 1m. 
Therefore ℓ=r2+h2−−−−−−√=0.04+1−−−−−−−√=1.04−−−−√=1.02
Curved surface of 1 cone =πrℓm2
                                                     =(3.14×.2×1.02)m2
Curved surface of such 50 cones =(50×3.14×.2×1.02)m2
Cost of painting @ Rs. 12 per m2 =(50×3.14×.2×1.02×12)
                                                                                        =384.68(approx)