Question 805107: 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 would you respond as a teacher? Will this technique always work?
