We have
Base of right circular cylinder = base of right circular cone = Base of hemisphere
∴   their radius are equal and their height are also equal
      So, the ratio of there volume’s is 
 ${\mathrm{\pi r}}^2\mathrm{h} : \frac{1}{3}{\mathrm{\pi r}}^2\mathrm{h} : \frac{2}{3}{\mathrm{\pi r}}^3$
       $1 : \frac{1}{3} : \frac{2}{3}$
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