用简便方法计算:1/(2*5)+1/(5*8)+1/(8*11)+1/(11*14)+1/(14*17)+1/(17*20)(其中/表示分数)

问题描述:

用简便方法计算:1/(2*5)+1/(5*8)+1/(8*11)+1/(11*14)+1/(14*17)+1/(17*20)(其中/表示分数)

1/3(1/2-1/5+1/5-1/8.+1/17-1/20)
=1/3(1/2-1/20)
=3/20