4/5×1/4+1/5×3/4=1/4*(4/5+3/5)=1/4*8/5=2/5
4/5×1/4+1/5×3/4=1/5×4/4+1/5×3/4=1/5×(1+3/4)=1/5×7/4=7/20
1/5*1/4(4+3)=1/20*7=7/20