Given sets A = {1, 3, 7}, B = {1, 3, 5, 9}, what is the union of A and B?

 A = {1, 3, 7}
 B = {1, 3, 5, 9}

The union is the set of all elements that belong to either set A or set B or both:

 A∪B={1,3,5,7,9}