A detective uses a converging lens of focal length 12 cm to examine the fine details of some cloth fibers found at the scene of a crime.  What is the maximum magnification given by the lens?

Here,  $f=12cm$
The maximum magnification occurs, when the image is formed by the lens at the least distance of distinct vision i.e. at D = 25 cm.
Therefore, maximum magnification given by the lens,
$M=1+\frac{D}{f}=1+\frac{25}{12}=1+2.1=3.1$