I will give a specific answer so that everyone can understand, and I hope that people who see my answer can promote my answer, and you are welcome to reject my answer!

Overview: This is not an economic question, but a values ??question.

First of all, when the seller exchanges the price of 50 yuan, the neighbor only acts as a tool for changing the change. From the beginning to the end, the neighbor has 0 income and 0 expenses. Therefore, the first thing is to remove the step of the neighbor exchanging money, which means that the seller does not exchange money or

I just went into the house and took 50 yuan in change from my wife.

Second: the buyer. The buyer finally paid 50 yuan or 10,000 yuan in counterfeit banknotes, which equals an expenditure of 0. He got a pair of shoes that cost 15 yuan and were worth 21 yuan.

I got another 29 yuan in change paid by the seller. The key is this. In terms of values, if you are the boss and the shoes are gone, do you feel that you have lost 15 yuan or 21 yuan?

So the answers 44 yuan and 50 yuan are both correct answers.

Because the value orientation is different.

Now let me overturn some of the answers. Many people directly answered 100 yuan, which is completely wrong. The idea is that the shoes are 21 yuan + the change is 29 yuan + the neighbor gave 50 yuan = 100, or the shoes are 15 yuan + 29 + 50 = 94.

There is no difference between the two answers.

If you use the answer of 94 yuan to overturn it, there is nothing wrong with the 15 yuan for the shoes. In fact, the 29 yuan was not given by the seller, but by the neighbor. In other words, the last one: "+50" includes the middle 29 yuan. (Do you understand?)

Okay, if you remove 29, you get 15+50=65 yuan, which is wrong again. Why?

If you imitate it yourself, you will find that you actually have 21 yuan in your hand, which is what is left over from the 50 yuan given by your neighbor to find a buyer, right?

So 65 minus 21 equals 44.

If you add in the 6 yuan that you should theoretically earn, it will be 44+6=50 yuan. Both answers are correct.

But my answer is neither of these two, because if you look at the last sentence, it proves that you are not suitable for playing funds!

So let me announce my formula: it is rare or never seen online. My understanding is that the transaction price of the shoes is actually 21 yuan. To put it bluntly, I just made 21 yuan less + got 29 yuan for free, which is 50 yuan.

My theoretical 50 yuan is gone.