|1/10-1/11|+|1/11-1/12|+…|1/19-1/20|

问题描述:

|1/10-1/11|+|1/11-1/12|+…|1/19-1/20|

|1/10-1/11|+|1/11-1/12|+…|1/19-1/20|
=1/10-1/11+1/11-1/12+…+1/19-1/20
=1/10-1/20
=1/20