The profit and loss of liquidation on the same day = (2050-2000) * 20 *10 =10000, that is, the income from buying 20 lots of soybean meal at 2000 yuan and selling it at 2050 yuan on the same day.

The profit and loss of positions held on that day =(2040-2000)*20* 10=8000, and the profit and loss of 20 lots still holding positions are calculated according to the settlement price of that day.

So the total profit and loss of customers on that day =10000+8000 =18000.