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Volumes of two spheres are in the ratio $64:27$. Find the ratio of their surface area.
Given: Volumes of two spheres are in the ratio $64:27$.
To do: To find the ratio of their surface area.
Solution:
To find the ratio of the surface areas, first we have to find the surface areas with their volumes.
Radius of big sphere $=R$
Radius of small sphere $=r$
Volume of bigger sphere$=\frac{4}{3}\pi R^3$
Volume of smaller sphere$=\frac{4}{3}\pi r^3$
Given, Volume of bigger sphere$:$Volume of smaller sphere $=64:27$
$\Rightarrow \frac{\frac{4}{3}\pi R^3}{\frac{4}{3}\pi r^3}=\frac{64}{27}$
$\Rightarrow \frac{R^3}{r^3}=\frac{64}{27}$
$\Rightarrow \frac{R}{r}=\sqrt[3]{\frac{64}{27}}$
$\Rightarrow \frac{R}{r}=\frac{4}{3}$
Surface area of bigger sphere$=4\pi R^2$
Surface area of smaller sphere$=4\pi r^2$
Hence, Surface area of bigger sphere: Surface area of smaller sphere$=\frac{4\pi R^2}{4\pi r^2}$
$=( \frac{R}{r})^2$
$=( \frac{4}{3})^2$
Thus, the ratio of their surface areas $=16:9$
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