A solid cylinder has a total surface area of $231 \mathrm{~cm}^{2}$. Its curved surface area is $\frac{2}{3}$ of the total surface area. Find the volume of the cylinder.
We know that the total surface area of the cylinder is 231 cm2 and the curved surface area is 2/3 of the total surface area.
So, the curved surface area is:
$2 / 3 \times\left(231 \mathrm{~cm}^{2}\right)=154 \mathrm{~cm}^{2}$
Then, the radius of the cylinder can be calculated in the following manner:
Curved surface area = 2πrh
154 cm2 = 2πrh ... (1)
Here, r cm is the radius of the cylinder and h cm is the length of the cylinder.
2πr2 = (231-154) cm2 = 77 cm2
77 cm2 = 2πr2
From here, the radius (r) can be calculated in the following manner:
$\boldsymbol{r}=\sqrt{\frac{77}{2 \times \frac{22}{7}}}$
r = 3.5 cm
Substituting this result into equation (1):
1
54 cm2 = 2π(3.5 cm)h
$h=154 \mathrm{~cm}^{2} /\left(2 \times \frac{22}{7} \times(3.5 \mathrm{~cm})\right)$
h = 7 cm
$\therefore V=\pi r^{2} h=\frac{22}{7} \times(3.5 \mathrm{~cm})^{2} \times(7 \mathrm{~cm})=269.5 \mathrm{~cm}^{3}$
Hence, the volume of the cylinder is 269.5 cm3.