Our opening quote contended that Venn diagrams are overrated. Even those who agree must admit that they have a curious allure. Take the sets of interesting topics in logic, in geometry and in ...

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.

It can help to write how many variables are in each set, so you don’t accidentally leave any out. Whenever possible, try to integrate rules right into your master diagram. So, if David doesn’t ...