An object is placed at 10 cm from a lens and real image is formed with magnification of 0.5. Then the lens is:

convex with focal length of 10/3 cm

Magnification m = $\frac{v}{u} = \frac{v}{-10} = -0.5 $

$\Rightarrow v = 5 cm$

$\frac{1}{f} = \frac{1}{v} - \frac{1}{u} = \frac{1}{5} - \frac{1}{-10} = \frac{3}{10} $

$\Rightarrow f = \frac{10}{3} cm$

Its a convex lens with focal length $\frac{10}{3}cm$