Final answer:
Mary is correct in stating that the equation (3ag + fh) + (-82xy) = 3ag +(fh + -82xy) demonstrates the associative property of addition. This property is shown by regrouping terms without affecting the sum.
Step-by-step explanation:
The student is asking if the equation (3ag + fh) + (-82xy) = 3ag +(fh + -82xy) demonstrates the associative property of addition. Mary is indeed correct. The associative property states that when adding three or more numbers, the way in which the numbers are grouped does not affect the sum. This property is illustrated here by regrouping the terms without changing the outcome of the addition. In the given equation, the parentheses are shifted from around 3ag and fh to around fh and -82xy, yet the equality remains true, which is consistent with the associative property.