$A$ person cannot see an object clearly if it is placed beyond $100 \, cm$. Find the power of the lens required to see an object clearly at infinity.

$A$ person who can see things most clearly at a distance of $10 \, cm$ requires spectacles to enable him to see clearly things at a distance of $30 \, cm$. What should be the focal length of the spectacles?

$A$ 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 $cm$?

$A$ person can see clearly only up to a distance of $25 \, cm$. He wants to read a book placed at a distance of $50 \, cm$. What kind of lens does he require for his spectacles and what must be its power?

The human eye has a lens which has a

$A$ person wears glasses of power $-2.5 \, D$. What is the far point of the person without glasses in $cm$?