设:甲桶原来有油x千克,则乙桶原来有油180-x千克.
(1-1/4)x:(1/4x+180-x)=1:2
3/4x:(180-3/4x)=1:2
3/2x=180-3/4x
9/4x=180
x=80
乙桶原来有油180-80=100(千克)