If the radius of curvature of a spherical mirror is 20 cm, what is its focal length ?

Explanation

Rear view mirrors should have a large field of view so that drivers can easily see most of the traffic behind them. Convex mirrors always form, diminished, erect, and virtual images of the objects.
Due to this property of forming diminished, erect, and virtual images, convex mirrors are preferred as rear-view mirrors.