|1/101－1/102|＋|1/102－1/103|＋|1/103－1/104|＋|1/104－1/105|
=1/101-1/102+1/102-1/103+1/103-1/104+1/104-1/105
=1/101-1/105
=4/(101*105)
=4/10605