6分之5+10分之9+6分之1
=(5/6+1/6)+9/10
=1+9/10
=9/10;
1-5分之3-5分之2
=1-(3/5+2/5)
=1-1
=0;
8分之5-12分之1+12分之5
=5/8+(5/12-1/12)
=5/8+4/12
=15/24+8/24
=23/24
4分之3-（12分之7-4分之1）
=3/4-7/12+1/4
=(3/4+1/4)-7/12
=1-7/12
=5/12;
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