Basic math and mechanics are flawed. Be very careful with building anything.

Three guys on a business trip decide to get a hotel room. It is $30 a night. Each pay 10$ and they get their room. The Hotel Manager realizes that it’s a sale event and the men should have only been charged $25. He gives an employee 5 one dollar bills to give back to the men. The employee is a thief and keeps two dollars. The men get $3 back. Now each man has spent 9$ instead of $10. 3x $9=$27. The thief kept 2$. 27+2= $29. Where did the other dollar go?