inclusion-exclusion principle

The inclusion-exclusion principle is a method used to calculate the size of a union of multiple sets while avoiding double counting. Imagine you want to find out how many people like either chocolate, vanilla, or both ice cream flavors. You first count those who like chocolate, then those who like vanilla. However, people who like both flavors were counted twice. To get the accurate total, you subtract the number of people who like both flavors. This principle helps ensure that every individual is counted only once, providing a clearer picture of the overall preferences.