2/3-1/6
=1/2
3/4+1/8
=7/8
6/7+7/9-6/7+7/9
=6/7-6/7+7/9+7/9
=0+14/9
=14/9
7/18*36-7/18
=14-7/18
=13又11/18
一题不要发真么多好不好,
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