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2
3
+
5
9
+
1
3
1
7
+
1
6
+
6
7
+
5
6
1
6
+
8
15
+
5
6
4
7
-
1
3
+
3
7
4
7
+
7
15
+
3
7
+
8
15
分析:(1)、(2)、(3)、(5)根据加法交换律和加法结合律进行计算比较简便;
(4)可利用加法交换律交换-
1
3
3
7
位置,然后再进行计算即可.
解答:解:(1)
2
3
+
5
9
+
1
3

=
2
3
+
1
3
+
5
9

=1+
5
9

=1
5
9


(2)
1
7
+
1
6
+
6
7
+
5
6

=(
1
7
+
6
7
)+(
5
6
+
1
6

=1+1
=2;

(3)
1
6
+
8
15
+
5
6

=
1
6
+
5
6
+
8
15

=1+
8
15

=1
8
15


(4)
4
7
-
1
3
+
3
7

=
4
7
+
3
7
-
1
3

=1-
1
3

=
2
3


(5)
4
7
+
7
15
+
3
7
+
8
15

=(
4
7
+
3
7
)+(
7
15
+
8
15

=1+1
=2.
点评:此题主要考查的是简便运算在分数加减法中的应用.
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