A person is in a room whose ceiling and two adjacent walls are mirrors. How many images are formed?

The walls will act as two mirrors inclined to each other at 90° and so will form  $\left(\frac{360}{90}-1\right)=4-1$ i.e. 3 images of the person. Now these images with person will act as objects for the ceiling mirror and so ceiling mirror will form  images further. Therefore total number of images formed = 3+3+1 = 7