Definition: A set is a group of distinct elements such as objects or numbers. The union of two sets (∪) is the set of elements that are in either set. The intersection of two sets (∩) is the set of elements that are in both sets.

Other set notation:
{ } set
| such that
A ⊆ B A is a subset of B

Example: Let A = {1, 2, 3}.  Let B = {0, 2, 4}.

Find A∩B.

Find A∪B.

Solution: 

To find the intersection, we compare the two sets and see which elements are in both sets.

A∩B = {2}

To find the union, we look at the two sets and list all of the elements that are in either set or both.

A∪B = {0, 1, 2, 3, 4}

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