A Venn diagram captioned: "In a survey of 250 European travelers ... The area of intersection is labeled 70. Funding for this project is provided by the National Science Foundation.

In set notation this is B = {1, 4, 9}. 30 people answered a survey about whether they have a dog or a cat. The Venn diagram shows the information from the survey. 13 people have got a dog.

Venn diagrams are used to sort sets of data. The probability of an event not happening uses the complement of the region on the Venn diagram. Count the number of elements in each region.