A fourth-grade student devised the following algorithm for subtracting 84 - 27: 4 minus 7 equals negative 3. 84 -27/-3 80 minus 20 equals 60. 84 -27/-3 60 60 plus negative 3 equals 57. 84 -27/-3 +60/57 Thus, the answer is 57. How should you respond as a teacher? Will this technique always work? An eighth-grade student claims she can prove that subtraction of integers is commutative. She Points out th