题目内容
巧算下面各题.
(1)60×(
+
+
+
)
(2)
×2
+0.125×4
+3×125%
(3)
×
+
×
(4)
+
+…+
+
.
(1)60×(
1 |
2 |
1 |
4 |
5 |
12 |
2 |
15 |
(2)
1 |
8 |
1 |
3 |
2 |
3 |
(3)
8 |
17 |
2 |
25 |
2 |
17 |
9 |
25 |
(4)
1 |
1×2 |
1 |
2×3 |
1 |
18×19 |
1 |
19×20 |
考点:分数的四则混合运算,分数的巧算
专题:运算顺序及法则
分析:(1)根据乘法分配律进行简算;
(2)根据乘法分配律进行简算;
(3)根据乘法分配律进行简算;
(4)根据分数的拆项进行简算.
(2)根据乘法分配律进行简算;
(3)根据乘法分配律进行简算;
(4)根据分数的拆项进行简算.
解答:
解:(1)60×(
+
+
+
)
=60×
+60×
+60×
+60×
=30+15+25+8
=45+25+8
=70+8
=78;
(2)
×2
+0.125×4
+3×125%
=0.125×2
+0.125×4
+3×0.125
=0.125×(2
+4
+3)
=0.125×10
=1.25;
(3)
×
+
×
=
×
+
×
=
×(
+
)
=
×
=
;
(4)
+
+…+
+
=(1-
)+(
-
)+…+(
-
)+(
-
)
=1-
+
-
+…+
-
+
-
=1-
=
.
1 |
2 |
1 |
4 |
5 |
12 |
2 |
15 |
=60×
1 |
2 |
1 |
4 |
5 |
12 |
2 |
15 |
=30+15+25+8
=45+25+8
=70+8
=78;
(2)
1 |
8 |
1 |
3 |
2 |
3 |
=0.125×2
1 |
3 |
2 |
3 |
=0.125×(2
1 |
3 |
2 |
3 |
=0.125×10
=1.25;
(3)
8 |
17 |
2 |
25 |
2 |
17 |
9 |
25 |
=
2 |
17 |
8 |
25 |
2 |
17 |
9 |
25 |
=
2 |
17 |
8 |
25 |
9 |
25 |
=
2 |
17 |
17 |
25 |
=
2 |
25 |
(4)
1 |
1×2 |
1 |
2×3 |
1 |
18×19 |
1 |
19×20 |
=(1-
1 |
2 |
1 |
2 |
1 |
3 |
1 |
18 |
1 |
19 |
1 |
19 |
1 |
20 |
=1-
1 |
2 |
1 |
2 |
1 |
3 |
1 |
18 |
1 |
19 |
1 |
19 |
1 |
20 |
=1-
1 |
20 |
=
19 |
20 |
点评:考查了运算定律与简便运算,四则混合运算.注意运算顺序和运算法则,灵活运用所学的运算定律简便计算.
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