A person uses a lens of power -2.0D for correcting his distant vision. For correcting his near vision he uses a lens of power +1.5D. What is the focal length of the lenses required to correct this disorder ?

A person needs two lenses to correct the disorder and these two lenses are convex lens for near vision and concave lens for distant vision. The relation between the focal length and the power for both the lenses will be,
 $f=\frac{1}{Power}$
On substituting the given values for both the lenses we get,
 $$\begin{gathered} f_{concave}=\frac{1}{-2.0 D}=-0.5 m=-50 cm \\ and \\ {f}_{convex}=\frac{1}{1.5 D}=0.67 m=67 cm \end{gathered}$$