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?jǐn)?shù)相加減,分子不變,分母相加減;
異分母分?jǐn)?shù)相加減,先通分,變成同分母的分?jǐn)?shù)相加減,再計(jì)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
點(diǎn)評(píng):本題屬于基本的計(jì)算,在平時(shí)都積累經(jīng)驗(yàn),逐步提高運(yùn)算的速度和準(zhǔn)確性.
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