$A$ person is able to see objects clearly only when these are lying at distances between $50\, cm$ and $300\, cm$ from his eye.
$(a)$ What kind of defect of vision is he suffering from?
$(b)$ What kind of lenses will be required to increase his range of vision from $25\, cm$ to infinity? Explain.

(N/A) For a normal eye,the near point is at $25\, cm$ and the far point is at infinity. The given person cannot see objects clearly closer than $50\, cm$ (near point defect) or farther than $300\, cm$ (far point defect). Therefore,he is suffering from both myopia (nearsightedness) and hypermetropia (farsightedness),a condition often referred to as presbyopia.
$(b)$ To correct these defects,a bifocal lens is required. $A$ concave lens of suitable focal length is used in the upper part to correct myopia (to see distant objects up to infinity),and a convex lens of suitable focal length is used in the lower part to correct hypermetropia (to see near objects up to $25\, cm$).