A compound microscope consists of an objective less of focal length $2.0\;cm$ and an eye -piece of focal legth $6.25\;cm$ , separated by a distance of 15 cm . How far from the objective should an object be placed in order to obtain the final image at the least distance of distinct vision (25 cm) . What is the magnifying power

Question

$\begin{array}{1 1} u_0=2.5\;cm\;m.p=20 \\ u_0=-2.5\;cm\;m.p=-20 \\ u_0=2.5\;cm\;m.p=2.5 \\u_0=20\;cm\;m.p=25 \end{array} $