At what distance in front of a concave mirror of focal length $30\; cm$,should an object be placed (in $cm$) so that its real image of size three times that of the object is obtained?

Two objects $A$ and $B$ are placed at $15\,cm$ and $25\,cm$ from the pole in front of a concave mirror having a radius of curvature $40\,cm$. The distance between the images formed by the mirror is $..........\,cm$.

The focal length of a concave mirror is $20 \ cm$. Determine where an object must be placed to form an image,magnified two times and real.

$A$ boy stands straight in front of a mirror at a distance of $30 \ cm$ away from it. He sees his erect image whose height is $\frac{1}{5}$ of his real height. The mirror he is using is

$A$ concave mirror of focal length $f$ produces a real image $n$ times the size of the object. The magnitude of the distance of the object from the mirror is:

The focal length $f$ is related to the radius of curvature $R$ of a spherical convex mirror by