There is no missing dollar in this equation. The ladies had already paid the bill of 30$ so they were -30$. The cashier then received the money which gave him +30$, which he then gave 5$ away so that left him +25$. The waiter was then +5$ and he gave the ladies all one dollar each which made them -27$. The waiter kept 2$ leaving him with a balance of +2$. If he would have returned the money the ladies would then have a balance of -25$. Therefore the cashier had his +25$ and the ladies were -25$, so there is no missing dollar.