Add whole numbers and you get another whole number.

Add integers and you get another integer.

Add two odd integers, and you get an even integer. This set is not closed under addition.

Add even integers and you get another even integer.

Add integers and you get another integer.

Add two odd integers, and you get an even integer. This set is not closed under addition.

Add even integers and you get another even integer.

**The set of odd integers is not closed under addition.**