题目内容
能简算的要简算．
0.25×1.25×0.8×0.4
87×
3600÷4÷9
375+450÷18×25
（
+
）÷
+
．
0.25×1.25×0.8×0.4
87×
| 3 |
| 86 |
3600÷4÷9
375+450÷18×25
（
| 4 |
| 5 |
| 1 |
| 4 |
| 7 |
| 3 |
| 7 |
| 10 |
考点：运算定律与简便运算
专题：运算定律及简算
分析：①0.25×1.25×0.8×0.4采用乘法的交换结合律，②采用把87分成86+1，利用乘法分配律，③3600÷4÷9=3600÷（4×9）采用交换结合律，④能想到把375分解35×15的形式，⑤采用有括号先算括号，然后再按运算顺序经行计算．
解答：
解：①0.25×1.25×0.8×0.4
=0.25×0.4×（1.25×8）
=0.1×1
=0.1
②87×
=（86+1）×
=86×
+1×
=3+
=3
③3600÷4÷9
=3600÷（4×9）
=3600÷36
=100
④375+450÷18×25
=375+25×25
=25×15+25×25
=25×（15+25）
=25×40
=1000
⑤（
+
）÷
+
=(
+
)÷
+
=
÷
+
=
+
=
=1
=0.25×0.4×（1.25×8）
=0.1×1
=0.1
②87×
| 3 |
| 86 |
=（86+1）×
| 3 |
| 86 |
=86×
| 3 |
| 86 |
| 3 |
| 86 |
=3+
| 3 |
| 86 |
=3
| 3 |
| 86 |
③3600÷4÷9
=3600÷（4×9）
=3600÷36
=100
④375+450÷18×25
=375+25×25
=25×15+25×25
=25×（15+25）
=25×40
=1000
⑤（
| 4 |
| 5 |
| 1 |
| 4 |
| 7 |
| 3 |
| 7 |
| 10 |
=(
| 16 |
| 20 |
| 5 |
| 20 |
| 7 |
| 3 |
| 7 |
| 10 |
=
| 21 |
| 20 |
| 7 |
| 3 |
| 7 |
| 10 |
=
| 9 |
| 20 |
| 14 |
| 20 |
=
| 23 |
| 20 |
=1
| 3 |
| 20 |
点评：寻找合适的运算律是解决问题的关键．
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