原题为
5/6-7/12+9/20-11/30+13/42-15/56+17/72
解=10/12-7/12+9/20-11/30+13/42-15/56+17/72
=3/12+9/20-11/30+13/42-15/56+17/72
=1/4+9/20-11/30+13/42-15/56+17/72
=5/20+9/20-11/30+13/42-15/56+17/72
=14/20-11/30+13/42-15/56+17/72
=7/10-11/30+13/42-15/56+17/72
=21/30-11/30+13/42-15/56+17/72
=10/30+13/42-15/56+17/72
=1/3+13/42-15/56+17/72
=14/42+13/42-15/56+17/72
=27/42-15/56+17/72
=9/14-15/56+17/72
=36/56-15/56+17/72
=21/56+17/72
=3/8+17/72
=27/72+17/72
=44/72
=11/18
因此,上式结果为十八分之十一.