20 33 49 65 29
-10 -20 -10 -30 -10
--- --- --- --- ---
10 13 39 35 19
39 31 55 77 68
-20 -10 -20 -40 -20
--- --- --- --- ---
19 21 35 37 48
NOTE:
Point out to the student that the digits in the one's column are subtracted
separately from the digits in the ten's column. Point out that any number
minus zero equals itself. Make up and solve a few more problems like these
with the student.