3 Use inclusionexclusion counting to find the number of diff

3. Use inclusion/exclusion counting to find the number of different ways that 5 students could exchange papers for grading so that each student grades exactly one paper, and no student grades his or her own paper.

the number of different ways that 5 students exchange papers:5!

and if no student his or her own paper then:4! way\'s we can arange.