Three friends have a nice meal together, and the bill is $25
The three friends pay $10 each, which the waiter gives to the Cashier
The Cashier hands back $5 to the Waiter
But the Waiter can't split $5 three ways, so he gives the friends one dollar each and keeps 2 dollars as a tip.
They all paid $10 and got $1 back. $10-$1 = $9
There were three of them 3 X $9 = $27
If they paid $27 and the waiter kept $2: $27+$2=$29
Where did the other dollar go? $30 - $1 = $29
...and you will also help the author collect more tips.
Interesting π