5×1/5÷5×4/5=1÷4=1/4
（8/9+2/3-2/27）×27= (8/9+6/9-2/27)×27=(14/9-2/27)×27=42-2=40
4/85÷1/86=4/85×86=344/85
9/17×1/7+5/17÷7=9/17×1/7+5/17×1/7=1/7×(9/17+5/17)=1/7×14/17=2/17