1/42＋1/56+1/72+1/90+1/110
=1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11
=1/6-1/11
=5/66
手机提问的朋友在客户端右上角评价点【满意】即可.