Associative property of addition

From Conservapedia

Basic addition is a pairwise operation. To add more than two numbers, you must combine them in pairs successively until all the numbers have been used. For example, to add X = 3 + 4 + 5 you first pick two consecutive numbers, say 3 and 4, and add them: X = 7 + 5. Now there are just two numbers remaining, which you can add to get the final answer: X = 12.

The associative property of addition is the fact that the answer does not depend on how the pairings are done. For example, we could have started with 4 + 5 = 9, and then done X = 3 + 9 = 12. We use parentheses to indicate the order of addition used. For example, writing (3 + 4) + 5 means that you first add 3 + 4 then add the result by 5. The associative property is expressed by the formula (3 + 4) + 5 = 3 + (4 + 5).

With more than three numbers, there can be many ways to do the addition. For example, with 4 numbers one of the ways is 2 + 3 + 4 + 5 = ((2 + 3) + 4) + 5 = (5 + 4) + 5 = 9 + 5 = 14.

The associative property of addition is different from the commutative property. For example, addition of matrices has the associative property but is not commutative. If A, B, and C are three matrices, then A + (B + C) = (A + B) + C but .