Mystrey??

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Three men goes to a hotel to stay ,the clerk says $30 per room/day so all the three plans to stay in one room so each pays $10.After some time the clerk realises that he made a mistake of collecting $30 but the room cost only $25,there fore he decides to return $5 to them so he calls the roomboy and gives him $5 asking him to return.The roomboy keeps $2 with him and he returns only $3($1 for each).Now Totally all have paid $9 each($27)+rommboy $2 which is equal to $27.where did $1 go,who has made the mistake?