$\text{p}=\frac{1}{\text{f}}=\frac{1}{0.08}=+1.25\text{D}$
$\text{p}=\frac{1}{\text{f}}=\frac{1}{0.5}=+2\text{D}$
Therefore, the light ray will be reflected back along the same path.
$\text{f}=\frac{\text{R}}{2}=\frac{20}{2}=10$
Hence, the focal length of the given spherical mirror is 10 cm.$\text{P}=\frac{1}{\text{f}}$
$\text{f}=\frac{1}{\text{P}}=\frac{1}{(-2)}=-0.5\text{m}=-50\text{cm}$
$\text{P}=\frac{1}{\text{f}}$
$\text{f}=\frac{1}{\text{P}}=\frac{1}{0.2}=+5\text{m}$
$\text{p}=\frac{1}{\text{f}}=\frac{1}{0.25}=+4\text{D}$

Or
$\frac{1}{\text{v}}+\frac{1}{\text{u}}=\frac{1}{\text{f}}$
v = distance of image from mirror.
u = distance of object from mirror.
f = focal length of mirror.


Virtual principal focus.
Real principal focus..