(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/[6.3-7/4*54/21]
=54/[6.3-27/6]
=54/[6.3-4.5]
=54/1.8
=30