1/2+5/6+11/12+19/20+29/30+41/42+55/56 =1-1/2+1-1/6+1-1/12+1-1/20+1-1/30+1-1/42+1-1/56 =7-(1/2+1/6+1/12+1/20+1/30+1/42+1/56) =7-(1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8) =7-(1-1/8) =6+1/8