When an object is placed $30\mathit{ cm}$ away from a convex lens of the focal length of $20\mathit{ cm}$. At what distance is the image of the object formed?

The image of the object formed at a distance of $60\mathit{ cm}$.
Here, $\mathrm{v}=? \mathrm{f}=20 \mathrm{cm}, \mathrm{u}=\mathrm{ }-30 \mathrm{cm}$,
From the lens formula, we get
$\frac{1}{\mathrm{v}}-\frac{1}{\mathrm{u}}=\frac{1}{\mathrm{f}}$        

$\Rightarrow \frac{1}{\mathrm{v}}=\frac{1}{20}+\frac{1}{-30}$
$\Rightarrow$  $\frac{1}{v}=\frac{3}{60}-\frac{2}{60}$
$\Rightarrow$ $\frac{1}{v}=\frac{1}{60}$
Therefore, $\mathit{v }= +60\mathit{ cm}$