甲:$\frac {1}{4}=\frac {2}{8}=\frac {3}{12}$
乙:$\frac {1}{6}=\frac {2}{12}$
丙:$\frac {1}{3}=\frac {2}{6}=\frac {3}{9}=\frac {4}{12}$
$ $因为$\frac {2}{12}<\frac {3}{12}<\frac {4}{12},$因此$\frac {1}{6}<\frac {1}{4}<\frac {1}{3}$
乙冷饮剩下的最少,则卖掉的最多,
所以下次应多批发乙冷饮。