设红毛衣进价x,黑毛衣进价y,则
(1+20%)x=30 x=25
(1-20%)y=30 y=37.5
两件毛衣进价
x+y=62.5
62.5-(30+30)=2.5
进价比卖出的钱还高2.5元,所以共亏两块五.