Wooden bowls

20 wooden bowls in the shape of a truncated cone should be painted on the outside and inside with wood varnish. We need 0.1 l of paint to paint 200 cm2. How many liters of paint do we have to buy if the bowls are 25 cm high, the bottom of the bowl has a diameter of 20 cm and the upper base has a diameter of 30 cm?

Correct result:

x =  46.3308 l

Solution:

n=20 ρ=0.1/200=12000=0.0005 l/cm2  h=25 cm d=20 cm D=30 cm  r=d/2=20/2=10 cm R=D/2=30/2=15 cm  S1=π r2=3.1416 102314.1593 cm2  S2=π (r+R) h2+(Rr)2=3.1416 (10+15) 252+(1510)22002.3803 cm2  S=S1+S2=314.1593+2002.38032316.5395  x=2 n ρ S=2 20 0.0005 2316.5395=46.3308 l



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