因为:x:y=3:5,y:z=2:3,所以:x=3y/5=0.6y,z=3y/2=1.5y
所以:(x+y-z):(2x-y+z)=(0.6y+y-1.5y):(1.2y-y+1.5y)=0.1y/1.7y=1/17