MAN, AGAIN!
I've answered this kind of question about... let me think, 50 times already.
I might be wrong (correct me if I am) but I think there are some mistakes in your question:
First, "i got a sunglass with a price 30$" means that you should be the one who pays for them, not your bros, so why did the worker return $1 each (what kind of worker is that)?
Second, I don't see the problem here. You said that there is $1 left, where? I don't see it. There is $5 discount, three of you each takes $1, and the worker takes $2, seems very reasonable to me. There is no $1 left. What $1 are you talking about?
Here is what I think the question should be (I make some changes in your original question):
"i went with my 2 brothers to a store, we got three sunglasses with a price of $10 each ($30 total) and then after we purchase it, the man in the store decided to make a discount by charging us $25 only. he send the worker to return the $5, he gave a$1 each , and there is $2 left with the worker but he decided to take it. So think. Each of us first paid $10 and get a $1 discount. So we only paid $9 each, which would make a total of $27. The worker kept $2. $27 + $2 = $29. But we first paid $30. Where does this $1 disappear?"
And here is how it fooled you:
The owner gave a $5 discount, which means that he only charged $25. The worker kept $2. Then it can be considered that the owner and the worker "charged" three of you a total of $27. The $2 of the worker is already included in this $27. There is no reason to add $2 to the total again.
sorry.