1-5/6+7/12-9/20+11/30-13/42+15/56
=1 - (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 - 1/2 + 1/8
=5/8