1 (1/3x+1/5y)/(2x-y)=[(5x+3y)/15]/(2x-y)=(5x+3y)/[(15(2x-y)]
2 (1/x)/(1/y)=y/x
3 (-a+b)/(a-b)=-(a-b)/(a-b)=-1
4 x/y=x/y