The near-point of a myopic person is $15 \mathrm{cm}.$ What should be the power of eye-glass so that the person can read clearly a book at a distance of $60 \mathrm{cm}$?

The ratio of the magnifying power of a convex lens used as a simple microscope when it is used to throw an image at the least distance of distinct vision to the magnifying power when it is used to throw an image at infinity is $6:5$ If the focal length of the lens is $4.8 \mathrm{cm}$, find the least distance of distinct vision.

In a microscope, the final image formed coincides with the object and is at least a distance of distinct vision $(25 \mathrm{cm})$ when the object is $4 \mathrm{cm}$ from the objective. Calculate the focal lengths of the objective and the eyepiece, assuming that the magnifying power of the microscope is $1.$