(1) 7/10+(4/5-1/4)/2又3/4 =7/10+(16-5)/20*4/11=7/10+1/5=9/10(2)[3/5-(9/10-2/5)]*1又1/7 =[3/5-1/2]*9/7=1/10*9/7=9/70(3)20.07*1994-19.93*2007=20.07*(1994-1993)=20.07(4)54/[6.3-1又3/4*(1又2/3+19/21)]=54/...