There are two key points.
1 cost 18 price 2 1
2 confusion 100 yuan
Many people are puzzled by 100+when calculating the total number of 100, because they borrowed100 from their neighbors and gave 79 to others. Actually, if you think about it carefully, who gave it to that person in 79 yuan? It is obviously the sum of 100 yuan-how is it possible?
The real loss is only 100 yuan borrowed from neighbors, which has nothing to do with finding out, while the goods are 18 yuan. After selling 2 1, they earned back 3 yuan, so the loss was actually 97 yuan.
You can also think that gold =-18 because the goods you buy are 18 yuan.
Others get 100 gold = 82.
Exchange gold with neighbors = 82
Find someone else 79 gold = 3 to sell things and earn 3 yuan.
The neighbor said it was fake and returned it to the neighbor with 100 gold = -97.