Answer :


Radius (r1) of upper end of container = 20 cm 

Radius (r2) of lower end of container = 8 cm


Height (h) of container = 16 cm


Slant height (l) of frustum = √((r1 - r2)2 + h2), 
where r1 and r2 (r1 > r2) are radii of frustum and h is height of frustum

=

=

= 20 cm


The capacity of container = Volume of a frustum


= h (r12 + r22 + r1r2)


= × 3.14 × 16 × [(20)2 + (8)2 + (20) (8)]


= × 3.14 × 16 (400 + 64 + 160)


= × 3.14 × 16 × 624


= 10449.92 cm3


= 10.45 litres


Cost of 1 litre milk = Rs 20


Cost of 10.45 litres milk = 10.45 × 20


= Rs 209


Area of metal sheet used to make the container = Curved surface area of frustum + area of lower base


= π (r1 + r2)  l + πr22


= π (20 + 8)  20 + π (8)2


= 560 π + 64 π


= 624 π cm2


Cost of 100 cm2 metal sheet = Rs 8


Cost of 624 π cm2 metal sheet =


= 156.75 Rs.

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