Question 1076545
A hollow cylinder has radius r cm and height 6r cm. 
3 spheres, also of radius r cm, are put into the cylinder. 
Work out the proportion of the cylinder that is not filled by the spheres.
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Cylinder:
{{{Vol = pi*r^2*h = 6pi*r^3}}}
3 spheres:
{{{Vol = 4pi*r^3}}}