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2
9
+
5
9
=
1-
4
7
=
3
8
+
1
4
=
7
8
-
3
8
=
4
5
+
2
3
=
3+
1
5
=
分析:同分母分数相加减,分母不变,分子相加减;
异分母分数相加减,先通分,化成同分母的分数,再计算.
解答:解:
2
9
+
5
9
=
7
9
1-
4
7
=
3
7
3
8
+
1
4
=
5
8
7
8
-
3
8
=
1
2
4
5
+
2
3
=
22
15
3+
1
5
=3
1
5
点评:根据分数加减法的计算方法进行计算,注意异分母分数相加减,要先通分,再计算.
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