题目内容
| 7 |
| 12 |
| 9 |
| 20 |
| 11 |
| 30 |
| 13 |
| 42 |
| 15 |
| 56 |
| 17 |
| 72 |
考点：分数的简便计算
专题：运算定律及简算
分析：观察每个分数可得
=
=
+
，-
=-
=-
-
，
=
=
+
，-
=-
=-
-
，
=
=
+
，-
=-
=-
-
，再相加即可．
| 7 |
| 12 |
| 7 |
| 3×4 |
| 1 |
| 3 |
| 1 |
| 4 |
| 9 |
| 20 |
| 9 |
| 4×5 |
| 1 |
| 4 |
| 1 |
| 5 |
| 11 |
| 30 |
| 11 |
| 5×6 |
| 1 |
| 5 |
| 1 |
| 6 |
| 13 |
| 42 |
| 13 |
| 6×7 |
| 1 |
| 6 |
| 1 |
| 7 |
| 15 |
| 56 |
| 15 |
| 7×8 |
| 1 |
| 7 |
| 1 |
| 8 |
| 17 |
| 72 |
| 17 |
| 8×9 |
| 1 |
| 8 |
| 1 |
| 9 |
解答：
解：原式=
+
-
-
+
+
-
-
+
+
-
-
=
-
=
．
故答案为：
．
| 1 |
| 3 |
| 1 |
| 4 |
| 1 |
| 4 |
| 1 |
| 5 |
| 1 |
| 5 |
| 1 |
| 6 |
| 1 |
| 6 |
| 1 |
| 7 |
| 1 |
| 7 |
| 1 |
| 8 |
| 1 |
| 8 |
| 1 |
| 9 |
=
| 1 |
| 3 |
| 1 |
| 9 |
=
| 2 |
| 9 |
故答案为：
| 2 |
| 9 |
点评：本题考查了分数的简便计算，关键是把每个分数化为两个分数的和．
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