An object is placed at a distance of 16 cm from a concave mirror. If the image is 20 times the object then find the image distance.

Object distance, u = -16 cm (Object distance is always taken as negative)
Magnification = 20
Image distance (v)?

We know that, Magnification=  $-\frac{\mathrm{v}}{\mathrm{u}}$
$\therefore 20 =\frac{-\text{v}}{-16}$

$\Rightarrow$ v = 320 cm

Therefore, the image distance will be 320 cm.