A solid cylinder has a total surface area of $231 \mathrm{~cm}^{2}$. Its curved surface area is 3 of the total surface area. Find the volume of the cylinder.
Given,
Total surface area $=231 \mathrm{~cm}^{2}$
Curved surface area = 2/3 * (total surface area)
= 2/3 * 231
= 154
We know that,
$2 \pi r h+2 \pi r^{2}=231 \ldots .1$
Here $2 \pi r h$ is the curved surface area, so substitute the value of CSA in eq 1
$\Rightarrow 154+2 \pi r^{2}=231$
$\Rightarrow 2 \pi r^{2}=231-154$
$\Rightarrow 2 \pi r^{2}=77$
$\Rightarrow 2^{*} 22 / 7^{*} r^{2}=77$
$\Rightarrow \mathrm{r}^{2}=\frac{77 * 7}{22 * 2}$
$\Rightarrow \mathrm{r}^{2}=\frac{7 * 7}{2 * 2}$
⟹ r = 7/2
We need to find the value of h
$C S A=154 \mathrm{~cm}^{2}$
⟹ 2πrh = 154
⟹ 2 * 22/7 * 7/2 * h = 154
⟹ h = 154/22
⟹ h = 7
So the volume of the cylinder is,
Volume $=\pi r^{2} h$
= 22/7 * 7/2 * 7/2 * 7
$=269.5 \mathrm{~cm}^{3}$
The volume of the cylinder is $269.5 \mathrm{~cm}^{3}$