(1)(+1/2)+(-1/2)+(-6/7)=0-6/7=-6/7(2)0.5+(-1/4)+0.75+(+1/2)=(0.5+1/2)+(-1/4+0.75)=1+0.5=1.5(3)1/4+(+5又3/5)+(-0.25)+(-3又1/8)=(1/4-0.25)+(5又3/5-3又1/8)=0+2又19/40=2又19/40 (4)-1.5+1.75+(-3.75)+(-1.5)=(-1.5-1.5)+(1.75-3.75)=-3-2=-5