<p>i'm a math and econ major, and i'd say the only advantage is that (i'm guessing) a lower percentage of applicants are math majors than econ, which could be a slight edge. being a math major has been infinitely more helpful than being an econ major.</p>
<p>Well, since UCLA doesn't evne look at your declared major when considering your application, I would say to major in (declare rather - you will probably change your mind later) what you want to do.</p>