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3
5
+
2
5
=
7
15
-
2
15
=
1
2
+
1
3
=
1
2
+4
=
1-
7
9
=
1
3
+
1
4
=
1
2
+
5
6
=
1
7
+
1
8
=
分析:同分母分数相加减,分子不变,分母相加减;
异分母分数相加减,先通分,变成同分母的分数相加减,再计算.
解答:解:
3
5
+
2
5
=1,
7
15
-
2
15
=
1
3

1
2
+
1
3
=
5
6

1
2
+4
=4
1
2

1-
7
9
=
2
9

1
3
+
1
4
=
7
12

1
2
+
5
6
=
4
3

1
7
+
1
8
=
15
56
点评:本题属于基本的计算,在平时都积累经验,逐步提高运算的速度和准确性.
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