题目内容
计算下面各题能简算的要简算．
①（
-
）÷
②
×3+
÷
③
+
+
+
④3-
×
-
．
①（
| 6 |
| 7 |
| 5 |
| 6 |
| 1 |
| 42 |
②
| 7 |
| 10 |
| 3 |
| 10 |
| 1 |
| 3 |
③
| 5 |
| 8 |
| 3 |
| 7 |
| 3 |
| 8 |
| 4 |
| 7 |
④3-
| 3 |
| 2 |
| 10 |
| 21 |
| 2 |
| 7 |
分析：①除以一个数等于乘这个数的倒数，然后利用乘法分配律即可简便计算，②同①，③可利用加法的交换律和结合律进行简便计算，④按运算顺序计算即可．
解答：解：①（
-
）÷
=（
-
）×42
=
×42-
×42
=36-35
=1；
②
×3+
÷
=
×3+
×3
=（
+
）×3
=1×3
=3；
③
+
+
+
=（
+
）+（
+
）
=1+1
=2；
④3-
×
-
．
=3-
-
=3-（
+
）
=3-1
=2．
| 6 |
| 7 |
| 5 |
| 6 |
| 1 |
| 42 |
=（
| 6 |
| 7 |
| 5 |
| 6 |
=
| 6 |
| 7 |
| 5 |
| 6 |
=36-35
=1；
②
| 7 |
| 10 |
| 3 |
| 10 |
| 1 |
| 3 |
=
| 7 |
| 10 |
| 3 |
| 10 |
=（
| 7 |
| 10 |
| 3 |
| 10 |
=1×3
=3；
③
| 5 |
| 8 |
| 3 |
| 7 |
| 3 |
| 8 |
| 4 |
| 7 |
=（
| 5 |
| 8 |
| 3 |
| 8 |
| 3 |
| 7 |
| 4 |
| 7 |
=1+1
=2；
④3-
| 3 |
| 2 |
| 10 |
| 21 |
| 2 |
| 7 |
=3-
| 5 |
| 7 |
| 2 |
| 7 |
=3-（
| 5 |
| 7 |
| 2 |
| 7 |
=3-1
=2．
点评：此题考查分数混合运算的简便算法．
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