A container made up of a metal sheet is in the form of a frustum of a cone of height 16 cm with radii of its lower and upper ends as 8 cm and 20 cm respectively. Find the cost of the metal sheet used, if it costs ₹ 5 per 100 cm2. (Take π = 3·14)
₹ 98
R = 20 cm, r = 8cm, h = 16 cm
slant height, l =√h2+(R−r)2
= √256+144 cm
= 20 cm
Surface area of the metal sheet used to make the container
= πl(R+r)+πr2=π{l(R+r)+r2}
= (3.14) ×{20×28+64}cm2
= (3.14) × 624 cm2
= 1959.36 cm2
Therefore, the cost of the metal sheet at rate of ₹5 per 100 cm2
= ₹1959.36 ×5100
= ₹ 98 (approx.)