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Learning Objectives
After completing this section, you should be able to:
- Determine the intersection of two sets.
- Determine the union of two sets.
- Determine the cardinality of the union of two sets.
- Apply the concepts of AND and OR to set operations.
- Draw conclusions from Venn diagrams with two sets.
The movie Yours, Mine, and Ours was originally released in 1968 and starred Lucille Ball and Henry Fonda. This movie, which is loosely based on a true story, is about the marriage of Helen, a widow with eight children, and Frank, a widower with ten children, who then have an additional child together. The movie is a comedy that plays on the interpersonal and organizational struggles of feeding, bathing, and clothing twenty people in one household.
If we consider the set of Helen's children and the set of Frank's children, then the child they had together is the intersection of these two sets, and the collection of all their children combined is the union of these two sets. In this section, we will explore the operations of union and intersection as it relates to two sets.
The Intersection of Two Sets
The members that the two sets share in common are included in the intersection of two sets. To be in the intersection of two sets, an element must be in both the first set and the second set. In this way, the intersection of two sets is a logical AND statement. Symbolically, intersection is written as: . intersection is written in set builder notation as: .
Let us look at Helen's and Frank's children from the movie Yours, Mine, and Ours. Helen's children consist of the set \(H=\{\) Colleen, Nick, Janette, Tommy, Jean, Phillip, Gerald, Theresa, Joseph\} and Frank's children are included in the set \(F=\{\) Mike, Rusty, Greg, Rosemary, Loise, Susan, Veronica, Mary, Germaine, Joan, Joseph \}. H intersection \(F\) is the set of children they had together. \(H \cap F=\{\) Joseph \(\}\), because Joseph is in both set \(H\) and set \(F\).
Example 1.23: Finding the Intersection of Set and Set
Set and Find intersection
- Answer
-
The intersection of sets and include the elements that set and have in common: 3, 5, and 7.
Your Turn 1.23
Set \(A=\{h, a, p, y\}\) and \(B=\{s, a, d\}\). Find \(A\) intersection \(B\).
Notice that if sets and are disjoint sets, then they do not share any elements in common, and intersection is the empty set, as shown in the Venn diagram below.