Answers

2014-03-12T20:15:50+05:30
To find volume of hollow cylinder.
The formula is volume =  \pi *(R^2 - r^2)*h
h = 21dm
Convert dm to cm so h = 21*10 = 210cm
R = 10/2 = 5cm
r = 6/2 = 3cm
 \pi = 22/7
Therefore, Volume = (22/7)*(5^2-3^2)*210
= 22*(25-9)*30 (cancelling 210 by 7)
=22*16*30 = 10560cu.cm(cm^3)
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2014-03-12T21:09:19+05:30
Volume of copper=volume of the hollow cylinder
volume of hollow cylinder= \pi R^2*h- \pi r^2*h(R=outer radius,r=inner radius,h=height)
R=10/2cm=5cm      r=6/2cm=3cm              h=21dm=210cm(1dm=10cm)
volume of copper= \pi *h(R^2-r^2)=22/7*210*(5^2-3^2)[210/7=30]
                                                             =22*30*(25-9)=660*16
                                                             =10506cu.cm
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