The inclusion/exclusion principle: counting unions

How to count the number of elements of a finite union of sets? This is quite easy when you deal with two sets: just count the number of elements of each of the sets and subtract the number of elements of their intersection (that was counted twice). How about with 3 sets, or even more? Carlo will explain it in the next video.

You can access the content of the video in the PDF file at the bottom of this step.