Union of Sets - Definition & Examples

Rodger did NOT make a mistake $\{1,2,3,3,5\}$ contains all of the numbers in either the first set or the second.

Rodger DID make a mistake. $\{1,2,3,3,5\}$ contains two $3$'s. Union sets do not contain more than one element that is the same. The union set is $\{1,2,3,5\}.$

Rodger DID make a mistake. He should not have put $\{\text{ }\}$'s around the numbers. He should just list them.