$A$ person cannot see distinctly at a distance less than $1 \, m$. Calculate the power of the lens that he should use to read a book at a distance of $25 \, cm$.

$A$ person has a near point of $50\, cm$. What lens should they use to reduce it to $25\, cm$?

$A$ person cannot see objects clearly placed at a distance of more than $40 \, cm$. He is advised to use a lens of power:

The far point of a myopic person is $80\, cm$ in front of the eye. What is the power of the lens required to enable him to see very distant objects clearly?

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

The least distance of distinct vision for a long-sighted person is $x \ m$. He wants to read a newspaper placed at a distance $(x/2) \ m$. The power of the spectacle lens used by him is $x \ D$. What is the value of $x$?