题目内容
看谁算得准(能简算要简算). ①
|
②1.05×(3.8-0.8)÷6.3 | ③
| ||||||||||||||
④2008×
|
⑤(
|
⑥
|
分析:①②③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;
④可将2008拆分为2007+1后再根据乘法分配律进行计算;
⑤可根据乘法分配律进行计算;
⑥可根据巧算公式
=
-
进行简便计算.
④可将2008拆分为2007+1后再根据乘法分配律进行计算;
⑤可根据乘法分配律进行计算;
⑥可根据巧算公式
1 |
n(n+1) |
1 |
n |
1 |
n+1 |
解答:解:①
÷5+
÷2
=
×
+
×
,
=
+
,
=
+
,
=
;
②1.05×(3.8-0.8)÷6.3,
=1.05×3÷6.3,
=3.15÷6.3,
=0.5;
③
÷[
×(
+
)]
=
÷[
×
],
=
×
,
=
;
④2008×
,
=(2007+1)×
,
=2007×
+1×
,
=2006+
,
=2006
;
⑤(
+
)×15×17,
=
×15×17+
×15×17
=17+30,
=47;
⑥
+
+
+…+
,
=(1-
)+(
-
)+(
-
)+…+(
-
),
=1-
+
-
+
-
+…+
-
,
=1-
,
=
;
7 |
8 |
7 |
8 |
=
7 |
8 |
1 |
5 |
7 |
8 |
1 |
2 |
=
7 |
40 |
7 |
16 |
=
14 |
80 |
35 |
80 |
=
49 |
80 |
②1.05×(3.8-0.8)÷6.3,
=1.05×3÷6.3,
=3.15÷6.3,
=0.5;
③
9 |
20 |
1 |
2 |
2 |
5 |
4 |
5 |
=
9 |
20 |
1 |
2 |
6 |
5 |
=
9 |
20 |
5 |
3 |
=
3 |
4 |
④2008×
2006 |
2007 |
=(2007+1)×
2006 |
2007 |
=2007×
2006 |
2007 |
2006 |
2007 |
=2006+
2006 |
2007 |
=2006
2006 |
2007 |
⑤(
1 |
15 |
2 |
17 |
=
1 |
15 |
2 |
17 |
=17+30,
=47;
⑥
1 |
1×2 |
1 |
2×3 |
1 |
3×4 |
1 |
99×100 |
=(1-
1 |
2 |
1 |
2 |
1 |
3 |
1 |
3 |
1 |
4 |
1 |
99 |
1 |
100 |
=1-
1 |
2 |
1 |
2 |
1 |
3 |
1 |
3 |
1 |
4 |
1 |
99 |
1 |
100 |
=1-
1 |
100 |
=
99 |
100 |
点评:完成此类题目要认真分析式中数据的特点及内在联系,然后选择合适的方法进行计算.
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