### Home > CCA > Chapter 3 > Lesson 3.2.4 > Problem 3-74

3-74.

Are the odd numbers a closed set under addition? Justify your conclusion.

A set of numbers is closed under an operation if the operation cannot be used with numbers from the set to get a number not in the set.

Can you add odd numbers together to get a number that is not odd?

Odd numbers are not a closed set under addition. Some examples: