The near point and far point of a normal human eye are respectively:

$A$ presbyopic patient has a near point of $30 \, cm$ and a far point of $40 \, cm$. The dioptric power of the corrective lens required for seeing distant objects is: (in $, D$)

$A$ man with defective eyes cannot see objects distinctly at a distance of more than $60 \, cm$ from his eyes. The power of the lens to be used will be:

$A$ person has been using spectacles of power $-1.0$ diopter for distant vision and a separate reading glass of power $+2.0$ diopters. What is the least distance of distinct vision for this person in $cm$?

$A$ man suffering from myopia can read a book placed at $10 \ cm$ distance. For reading the book at a distance of $60 \ cm$ with relaxed vision,the focal length of the lens required will be ...... $cm$.

$A$ person can see objects clearly only when they lie between $50\, cm$ and $400\, cm$ from his eyes. In order to increase the maximum distance of distinct vision to infinity, the type and power of the correcting lens the person has to use will be