1-5/6+7/12-9/20+11/30-13/42+15/56-17/72+19/90=1/6+7/12-9/20+11/30-13/42+15/56-17/72+19/90=1/2-1/3+1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7+1/7+1/8-1/8-1/9+1/9+1/10=1/2+1/10=(5+1)/10=6/10=3/5
