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20-1 subtraction facts
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1-1
0
2-1
1
3-1
2
4-1
3
5-1
4
6-1
5
7-1
6
8-1
7
9-1
8
10-1
9
2-2
0
3-2
1
4-2
2
5-2
3
6-2
4
7-2
5
8-2
6
9-2
7
10-2
8
3-3
0
4-3
1
5-3
2
6-3
3
7-3
4
8-3
5
9-3
6
10-3
7
4-4
0
5-4
1
6-4
2
7-4
3
8-4
4
9-4
5
10-4
6
5-5
0
6-5
1
7-5
2
8-5
3
9-5
4
10-5
5
7-6
1
8-6
2
9-6
3
10-6
4
8-7
1
9-7
2
10-7
3
9-8
1
10-8
2
10-9
1
11-1
10
11-2
9
11-3
8
11-4
7
11-5
6
11-6
5
11-7
4
11-8
3
11-9
2
11-10
1
11-0
11
12-1
11
12-2
10
12-3
9
12-4
8
12-5
7
12-6
6
12-7
5
12-8
4
12-9
3
12-10
2
12-11
1
12-12
0
13-1
12
13-2
11
13-3
10
13-4
9
13-5
8
13-6
7
13-7
6
13-8
5
13-9
4
13-10
3
13-9
2
13-12
1
13-13
0
14-1
13
14-2
12
14-3
11
14-4
10
14-5
9
14-6
8
14-7
7
14-8
6
14-9
5
14-10
4
14-11
3
14-12
2
14-13
1
14-14
0
15-1
14
15-2
13
15-3
12
15-4
11
15-5
10
15-6
9
15-7
8
15-8
7
15-9
6
15-10
5
15-11
4
15-12
3
15-13
2
15-14
1
15-15
0
16-1
15
16-2
14
16-3
13
16-4
12
16-5
11
16-6
10
16-7
9
16-8
8
16-9
7
16-10
6
16-11
5
16-12
4
16-13
3
16-14
2
16-15
1
16-16
0
17-1
16
17-2
15
17-3
14
17-4
13
17-5
12
11-4
7
17-5
12
17-6
11
17-7
10
17-8
9
17-9
8
17-10
7
17-11
6
17-12
5
17-13
4
17-14
3
17-15
2
17-16
1
17-17
0
18-1
17
18-2
16
18-3
15
18-4
14
18-5
13
18-6
12
18-7
11
18-8
10
18-9
9
18-10
8
18-11
7
18-12
6
18-13
5
18-14
4
18-15
3
18-16
2
18-17
1
18-18
0
19-1
18
19-2
17
19-3
16
19-4
15
19-5
14
19-6
13
19-7
12
19-8
11
19-9
10
19-10
9
19-11
8
19-12
7
19-13
6
19-14
5
19-15
4
19-16
3
19-17
2
19-18
1
19-19
0
20-1
19
20-2
18
20-3
17
20-4
16
20-5
15
20-6
14
20-7
13
20-8
12
20-9
11
20-10
10
20-11
9
20-12
8
20-13
7
20-14
6
20-15
5
20-16
4
20-17
3
20-18
2
20-19
1
20-20
0
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