Aimee must add together the following numbers:
3.50 + 4.00 + (-1.25) + (-7.50) + 5.25 + 2.00
As her first step, Aimee writes:
(3.50 + (-7.50)) + (-1.25 + 5.25) + (4.00 + 2.00)
Which is the best explanation of what Aimee did in this step?