Three people eat at a hotel. The bill turned out to be $30. Each person paid $10. The clerk later finds that the bill is only $25. He sends an assistant to return the $5 to the 3 people. The assistant returns $1 to each of the 3 people and keeps $2 to himself. Now each person has effectively paid $9, thus a total of $27 was paid. In addition the assistant has $2. $27+$2=$29. But we started with $30. Where is the missing dollar?
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