题目内容
(2007?奉化市)用递等式计算.
①8
-(2
+3
)
②2.5÷8+3.5×
+0.125
③4.8-4.248÷(1.2+3
×1
)
④6.5×
+5.5÷1
⑤[5
-1.2×(
+1.5)]÷37.
①8
1 |
7 |
3 |
4 |
1 |
7 |
②2.5÷8+3.5×
1 |
8 |
③4.8-4.248÷(1.2+3
3 |
5 |
2 |
3 |
④6.5×
7 |
12 |
5 |
7 |
⑤[5
4 |
5 |
1 |
4 |
分析:算式①可根据一个数减两个数的和等于用这个数分别减这两个数的减法性质与交换律进行简便计算;
算式②④可根据乘法分配律进行简便计算;
算式③⑤根据四则混合运算的运算顺序计算即可:先算乘除,再算加减,有括号的要先算括号里面的;
算式②④可根据乘法分配律进行简便计算;
算式③⑤根据四则混合运算的运算顺序计算即可:先算乘除,再算加减,有括号的要先算括号里面的;
解答:解:①8
-(2
+3
)
=8
-3
-2
,
=5-2
,
=2
;
②2.5÷8+3.5×
+0.125
=2.5×
+3.5×
+
,
=(2.5+3.5+1)×
=7×
=
;
③4.8-4.248÷(1.2+3
×1
)
=.8-4.248÷(1.2+
×
),
=4.8-4.248÷(1.2+6),
=4.8-4.248÷7.2,
=4.8-0.59,
=4.21;
④6.5×
+5.5÷1
,
=6.5×
+5.5×
,
=(6.5+5.5)×
,
=12×
,
=7;
⑤[5
-1.2×(
+1.5)]÷37
=[55.8-1.2×(0.25+1.5)]÷37,
=[5.8-1.2×1.75]÷37,
=[5.8-2.1]÷37,
=3.7÷37,
=0.1.
1 |
7 |
3 |
4 |
1 |
7 |
=8
1 |
7 |
1 |
7 |
3 |
4 |
=5-2
3 |
4 |
=2
1 |
4 |
②2.5÷8+3.5×
1 |
8 |
=2.5×
1 |
8 |
1 |
8 |
1 |
8 |
=(2.5+3.5+1)×
1 |
8 |
=7×
1 |
8 |
=
1 |
8 |
③4.8-4.248÷(1.2+3
3 |
5 |
2 |
3 |
=.8-4.248÷(1.2+
18 |
5 |
5 |
3 |
=4.8-4.248÷(1.2+6),
=4.8-4.248÷7.2,
=4.8-0.59,
=4.21;
④6.5×
7 |
12 |
5 |
7 |
=6.5×
7 |
12 |
7 |
12 |
=(6.5+5.5)×
7 |
12 |
=12×
7 |
12 |
=7;
⑤[5
4 |
5 |
1 |
4 |
=[55.8-1.2×(0.25+1.5)]÷37,
=[5.8-1.2×1.75]÷37,
=[5.8-2.1]÷37,
=3.7÷37,
=0.1.
点评:当算式中同时含有分数与小数时,要根据式中数据的特点灵活将它们互化后再进行计算.
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