最后确定没打错?
1/1×4+1/4×7+1/7×10+1/10×13+1/13*16
=1/3*(1-1/4)+1/3*(1/4-1/7)+1/3*(1/7-1/10)+1/3*(1/10-1/13)+1/3*(1/13-1/16)
=1/3*[(1-1/4)+(1/4-1/7)+(1/7-1/10)+(1/10-1/13)+(1/13-1/16)]
=1/3*(1-1/16)
=1/3*15/16
=5/16