Daily profit and loss refers to the profit and loss at daily settlement, and individual profit and loss refers to the profit and loss at each opening and closing. The calculation method is as follows:

Calculate daily profit and loss:

Profit and loss on the first day: (2742-2740) × 50 = 100 yuan (profit)

Daily profit and loss of the next day: (2740-2740) × 50 = 0 yuan (even number).

Daily profit and loss on the third day: (2730-2740) × 50 = -500 yuan (loss)

Therefore, the daily profit and loss of this transaction is: 100 yuan -0 yuan -500 yuan = -400 yuan (loss).

Calculate personal profit and loss:

The profit and loss of the first transaction is: (2742-2740) × 50 = 100 yuan (profit).

The profit and loss of the second transaction is: (2740-2740) × 50 = 0 yuan (flat).

The profit and loss of the third transaction is (2730-2740) × 50 = -500 yuan (loss).

So the profit and loss of this transaction is: 100 yuan +0 yuan -500 yuan = -400 yuan (loss).

The result of profit and loss calculation should be the same as that of daily profit and loss calculation. The reason for the difference may be that you have some differences in details when calculating. As for 20 yuan, whose profit and loss is more than the daily profit and loss, it may be because you missed a transaction or made a mistake in calculation. You can carefully check the profit and loss of each transaction and recalculate.