20以减法练习题（破十法）
进位加法（凑十法口诀：看大数，分小数，凑成十，算得数。） 退位减法（破十法口诀：看大数，分出10，减小数，加剩数。）
例：15 — 8 = 7 5 10 2
18 — 9 = 17
15 — 9 = 14
— 9 = 16 — 9 = 13 — 9 = — 9 =
12 — 9 = 11 — 9 = 17 — 8 =
16 — 8 = 15
13 — 8 = 12
16 — 7 = 15
— 8 = 14 — 8 = 11 — 7 = 14 — 8 = — 8 = — 7 =
13 — 7 = 12 — 7 = 11 — 7 =
15 — 6 = 14
12 — 6 = 11
13 — 5 = 12
— 6 = 13 — 6 = 14 — 5 = 11 — 6 = — 5 = — 5 =
13 — 4 = 12 — 4 = 11 — 4 =
12 — 3 = 11
13 — 5 = 12
— 3 = 11 — 5 = 11 — 2 = — 5 =
13 — 4 = 12 — 4 = 11 — 4 =
16 — 7 = 15
18 — 9 = 17
15 — 9 = 14
— 7 = 14 — 9 = 16 — 9 = 13 — 7 = — 9 = — 9 =
13 — 7 = 12 — 7 = 11 — 7 =
12 — 9 = 11
16 — 8 = 15
— 9 = 17 — 8 = 14 — 8 = — 8 =
13 — 4 = 12 — 4 = 11 — 4 =
12 — 3 = 11
13 — 5 = 12
13 — 8 = 12
— 3 = 11 — 5 = 11 — 8 = 11 — 2 = — 5 = — 8 =
16 — 7 = 15 — 7 = 14 — 7 =
12 — 6 = 11
15 — 9 = 14
— 6 = 14 — 9 = 13 — 5 = — 9 =
13 — 4 = 12 — 4 = 11 — 4 =
12 — 3 = 11
13 — 5 = 12
13 — 8 = 12
— 3 = 11 — 5 = 11 — 8 = 11 — 2 = — 5 = — 8 =
16 — 7 = 15 — 7 = 14 — 7 =
12 — 6 = 11
15 — 9 = 14
— 6 = 14 — 9 = 13 — 5 = — 9 =
13 — 4 = 12 — 4 = 11 — 4 =
16 — 7 = 15
18 — 9 = 17
15 — 9 = 14
— 7 = 14 — 9 = 16 — 9 = 13 — 7 = — 9 = — 9 =
13 — 7 = 12 — 7 = 11 — 7 =
12 — 9 = 11
16 — 8 = 15
— 9 = 17 — 8 = 14 — 8 = — 8 =
13 — 4 = 12 — 4 = 11 — 4 =
16 — 7 = 15
18 — 9 = 17
15 — 9 = 14
— 7 = 14 — 9 = 16 — 9 = 13 — 7 = — 9 = — 9 =
13 — 7 = 12 — 7 = 11 — 7 =
12 — 9 = 11
16 — 8 = 15
— 9 = 17 — 8 = 14 — 8 = — 8 =
13 — 4 = 12 — 4 = 11 — 4 =
12 — 3 = 11
13 — 5 = 12
13 — 8 = 12
— 3 = 11 — 5 = 11 — 8 = 11 — 2 = — 5 = — 8 =
16 — 7 = 15 — 7 = 14 — 7 =
12 — 6 = 11
15 — 9 = 14
— 6 = 14 — 9 = 13 — 5 = — 9 =
13 — 4 = 12 — 4 = 11 — 4 =
12 — 3 = 11
13 — 5 = 12
13 — 8 = 12
— 3 = 11 — 5 = 11 — 8 = 11 — 2 = — 5 = — 8 =
16 — 7 = 15 — 7 = 14 — 7 =
12 — 6 = 11
15 — 9 = 14
— 6 = 14 — 9 = 13 — 5 = — 9 =
13 — 4 = 12 — 4 = 11 — 4 =
16 — 7 = 15
18 — 9 = 17
15 — 9 = 14
— 7 = 14 — 9 = 16 — 9 = 13 — 7 = — 9 = — 9 =
13 — 7 = 12 — 7 = 11 — 7 =
12 — 9 = 11
16 — 8 = 15
— 9 = 17 — 8 = 14 — 8 = — 8 =
13 — 4 = 12 — 4 = 11 — 4 =
16 — 7 = 15
18 — 9 = 17
15 — 9 = 14
— 7 = 14 — 9 = 16 — 9 = 13 — 7 = — 9 = — 9 =
13 — 7 = 12 — 7 = 11 — 7 =
12 — 9 = 11
16 — 8 = 15
— 9 = 17 — 8 = 14 — 8 = — 8 =
13 — 4 = 12 — 4 = 11 — 4 =
12 — 3 = 11
13 — 5 = 12
13 — 8 = 12
— 3 = 11 — 5 = 11 — 8 = 11 — 2 = — 5 = — 8 =
16 — 7 = 15 — 7 = 14 — 7 =
12 — 6 = 11
15 — 9 = 14
— 6 = 14 — 9 = 13 — 5 = — 9 =
13 — 4 = 12 — 4 = 11 — 4 =
12 — 3 = 11
13 — 5 = 12
13 — 8 = 12
— 3 = 11 — 5 = 11 — 8 = 11 — 2 = — 5 = — 8 =
16 — 7 = 15 — 7 = 14 — 7 =
12 — 6 = 11
15 — 9 = 14
— 6 = 14 — 9 = 13 — 5 = — 9 =
13 — 4 = 12 — 4 = 11 — 4 =
16 — 7 = 15
18 — 9 = 17
15 — 9 = 14
— 7 = 14 — 9 = 16 — 9 = 13 — 7 = — 9 = — 9 =
13 — 7 = 12 — 7 = 11 — 7 =
12 — 9 = 11
16 — 8 = 15
— 9 = 17 — 8 = 14 — 8 = — 8 =