/0.3/+/-0.2/ =0.3+0.2=0.5/三分之二/—/-二分之一/ =2/3-1/2=4/6-3/6=1/6/-1.75/×/负七分之二/ =1.75×2/7=(1+3/4)×2/7=7/4×2/7=1/2
问题不详,无法解答