The ratio between the radius of the base and the height of a cylinder is 2 : 3. If its volume is 1617 cm3,
Question:
The ratio between the radius of the base and the height of a cylinder is 2 : 3. If its volume is 1617 cm3, then its total surface area is
(a) 308 cm2
(b) 462 cm2
(c) 540 cm2
(d) 770 cm2
Solution:
(d) 770 cm2
We have:
r: h = 2 : 3
$\Rightarrow \frac{r}{h}=\frac{2}{3}$
$\Rightarrow h=\frac{3}{2} r$
Now, volume $=1617 \mathrm{~cm}^{3}$
$\Rightarrow \pi r^{2} h=1617$
$\Rightarrow \frac{22}{7} \times r^{2} \times \frac{3}{2} r=1617$
$\Rightarrow r^{3}=\frac{1617 \times 14}{66}=343$
$\Rightarrow r=7 \mathrm{~cm}$
∴ h = 10.5 cm
Hence, total surface area $=2 \pi r h+2 \pi r^{2}$
$=\frac{22}{7}\left(2 \times 7 \times 10.5+2 \times 7^{2}\right)$
$=\frac{22}{7}(147+2 \times 49)$
$=\frac{22}{7} \times 245$
$=770 \mathrm{~cm}^{2}$