四分之三减七分之二加四分之一加七分之五=(3/4)-(2/7)+(1/4)-(5/7)=(3/4)+(1/4)-(2/7)-(5/7)=[(3/4)+(1/4)]-[(2/7)+(5/7)]=1-1=0
3/4-2/7+1/4+5/7=(3/4+1/4)+(5/7-2/7)=1+3/7=10/7
3/4-2/7+1/4+5/7=(3/4+1/4)+(5/7-2/7)=1+3/7