For the first kind of clothes, the price is 100%+20%= 120% and the price is 120 yuan, so the cost is120 ÷120% =100. For the second kind of clothes, the price is 100%-20%=80%, and the price is 120 yuan, so the cost is 120÷80%= 150 yuan; So the first dress earned 120- 100 = 20 yuan, and the second dress lost 150- 120 = 30 yuan. If you calculate the general ledger, you will lose 10 yuan.

Money earned =120-120 ÷ (100%+20%) = 20 yuan.

Loss amount =120-120 ÷ (100%-20%) = 30 yuan.

Loss =30-20= 10 yuan.