1.{1/2-(3/4-3/5)}÷7/10 = ( 1/2-3/20)÷7/10 = 7/20÷7/10 =1/2 2.1-3x/4=3/5 3x/4=1-3/5 3x/4=2/5 x=2/5×(4/3) x=8/15 3 .x-x/4=3/8 x(1-1/4)=3/8 3x/4=3/8 x=3/8×(4/3) x=1/2