Subtracting Number From Itself

Gap-fill exercise

Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!
0-0=
1-1=
2-2=
3-3=
4-4=
5-5=
6-6=
7-7=
8-8=
9-9=
10-10=
11-11=
12-12=
13-13=
14-14=
15-15=
16-16=
17-17=
18-18=