An erect image is seen of $\large\frac{1}{5}$ th the height of the object kept at a distance of $20 \;cm$ from a mirror. The mirror must be :

(a)plane mirror

(b)concave mirror

(c)convex mirror

(d)Plano concave mirror

Small image is formed only by convex mirror , plane mirror forms image of same size, concave mirror forms image bigger then object.
Then it is the convex mirror.
Hence 'c' is the correct option

edited Jul 15, 2014