=1/2×5+3+1/5×8+5+1/8×11+7+1/11×14+9+1/14×17
=(3+5+7+9)+(1/2×5+1/5×8+1/8×11+1/11×14+1/14×17)
=24+1/3(3/2×5+3/5×8+3/8×11+3/11×14+3/14×17)
=24+1/3(1/2-1/5+1/5-1/8+1/8-1/11+1/11-1/14+1/14-1/17)
=24+1/3×15/34
=24又5/34