Chapter 5 - Number Theory and the Real Number System - 5.5 Real Numbers and Their Properties; Clock Addition - Exercise Set 5.5 - Page 308: 13

4 should go in the blank. The problem should read: 3 + (4 + 5) = 3 + (5 + 4)

The commutative property of addition states that numbers may be added in any order without changing the value of the end result (answer). To show this: 3 + (4 + 5) = 3 + (5 + 4) First parentheses (ALWAYS FOLLOW ORDER OF OPERATIONS) 3 + (9) = 3 + (9) 12 = 12