设原长为X米.x-(x/2+3)-{[x-(x/2+3)]/2+5}=6x-0.5x-3-[(x-0.5x-3)/2+5]=60.5x-3-(0.5x-0.25x-1.5+5)=60.5x-3-(0.25x+3.5)=60.5x-0.25x-3-3.5=60.25x=12.5x=50
