计算1/（6*11）+1/（11*16）+1/（16*21）+1/（21*26）+1/（26*31）+1/（31*36）

1/（6*11）+1/（11*16）+1/（16*21）+1/（21*26）+1/（26*31）+1/（31*36）
=1/5*(1/6-1/11)+1/5*(1/11-1/16)+1/5*(1/16-1/21)+1/5*(1/21-1/26)+1/5*(1/26-1/31)+1/5*(1/31-1/36)
=1/5*(1/6-1/11+1/11-1/16+1/16-1/21+1/21-1/26+1/26-1/31+1/31-1/36)
=1/5*(1/6-1/36)
=1/5*(6/36-1/36)
=1/5*5/36
=1/36