Carmen used the associative property of addition to solve the given problem.
The associative property means one can add or multiply the given numbers regardless of how they are grouped. In other words, if one is adding or multiplying it does not matter where the brackets are placed.
The given problem is -
17 + (45 + 23), 17 + (23 + 45), (17 + 23) + 45
So here the sum of all the three patterns is 85. This clearly proves that forming groups does not affect the sum. So this is based on associative property of addition.
