Question

Which property in math is (n+2.9)+0.3=n+(2.9+0.3)

Answer 1

Notice that the order the numbers are written on both sides is the same:

n, then 2.9, then 0.3

Because the order is the same and all that changed were the parentheses (the way the numbers were grouped), this is the associative property of addition.

The associative property is about the groupings. You can remember this by thinking about that fact that associations are groups.