简便运算,脱式,谢,有好评

(1)=(2/5+1/5)+(3/4+1/4)
=(3/5)+1
=8/5
(2)=3/8-1/4-1/8
=(3/8-1/8)-1/4
=1/4-1/4
=0
(3)=2/5+1/2-2/5
=1/2
(4)=7/8-1/8-1/4
=3/4-1/4
=1/2