1/5*8+1/8*11+1/11*14+1/14*17+1/17*20=?怎样算
问题描述：
1/5*8+1/8*11+1/11*14+1/14*17+1/17*20=?怎样算
答
1/(5*8)=(1/3)*(1/5-1/8)
1/(8*11)=(1/3)*(1/8-1/11)
其他项同理
原式=(1/3)*(1/5-1/8+1/8-1/11+...+1/17-1/20)
=(1/3)*(1/5-1/20)
=1/20