题目内容
用简便方法计算下面各题．
3.1+2.4+1.9+3.6
4.2×99+4.2
24×（
+
）
÷
+
×
．
3.1+2.4+1.9+3.6
4.2×99+4.2
24×（
| 3 |
| 8 |
| 5 |
| 6 |
| 7 |
| 9 |
| 11 |
| 5 |
| 5 |
| 11 |
| 2 |
| 9 |
①3.1+2.4+1.9+3.6
=（3.1+1.9）+（2.4+3.6）
=5+6
=11；
②4.2×99+4.2
=4.2×（99+1）
=4.2×100
=420；
③24×（
+
）
=24×
+24×
=9+20
=29；
④
÷
+
×
=
×
+
×
=
×（
+
）
=
×1
=
．
=（3.1+1.9）+（2.4+3.6）
=5+6
=11；
②4.2×99+4.2
=4.2×（99+1）
=4.2×100
=420；
③24×（
| 3 |
| 8 |
| 5 |
| 6 |
=24×
| 3 |
| 8 |
| 5 |
| 6 |
=9+20
=29；
④
| 7 |
| 9 |
| 11 |
| 5 |
| 5 |
| 11 |
| 2 |
| 9 |
=
| 7 |
| 9 |
| 5 |
| 11 |
| 5 |
| 11 |
| 2 |
| 9 |
=
| 5 |
| 11 |
| 7 |
| 9 |
| 2 |
| 9 |
=
| 5 |
| 11 |
=
| 5 |
| 11 |
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