(-2.5)+(-3又1/2)+(-1又3/4)+3+(-1又1/4)=-(2.5+3又1/2)-(1又3/4+1又1/4)+3=-6-3+3=-6
(-2.5)+(-3又1/2)+(-1又3/4)+3+(-1又1/4)=-2.5-3.5-1.75+3-1.25=-(2.5+3.5)-(1.75+1.25)+3=-6-3+3=-6