1+1/2-5/6+7/12-9/20+11/30-13/42
=1+1/2-5/6+1-5/12+1-11/20+11/30-13/42
=1+1/2+1-5/4+1-11/60-13/42
=3-3/4-11/60-13/42
=3-14/15-13/42
=3-87/70
=1又53/70
1+1/2-5/6+7/12-9/20+11/30-13/42
=1+1/2-5/6+1-5/12+1-11/20+11/30-13/42
=1+1/2+1-5/4+1-11/60-13/42
=3-3/4-11/60-13/42
=3-14/15-13/42
=3-87/70
=1又53/70