Associative property of mathematical addition of integers

The associative property of mathematical addition of integers says that any order of grouping of numbers in addition/summation results into same answer. 
The associative property of mathematical addition of integers can be represented as following

(a + b) + c = a + (b + c)

To understand associative property of mathematical addition of integers we can try adding numbers in different orders and note the results. 
For example,

If a = 5, b = 3 and c = 7

Then (5 + 3) + 7 = 15 and 5 + (3 + 7) = 15

So, (5 + 3) + 7 = 5 + (3 + 7) as 15 = 15

 
Another example,

If a = 5, b = -3 and c = 7

Then (5 + (-3)) + 7 = 9 and 5 + ((-3) + 7) = 9

So, (5 + (-3)) + 7 = 5 + ((-3) + 7) as 9 = 9