Three guys went to a hotel and gave $30 to the server to buy hamburgers. It happened that on that day, the fast food chain store had a special offer `3 hamburgers for $1!' The server took advantage of that, getting $29 and three hamburgers in return. He kept $26 as his tip, and returned $3 of change and three hamburgers to the guests.
So the guests spent $27 for the hamburgers and $26 as tip, i.e., $53 in total, which was $23 more than the original $30. Where did the extra money come from!
I hope you find it totally trivial and silly. If so, the `missing dollar' problem is just the same, except with different parameters. The food was a pizza, the store price was $25, and the tip was $2. That's all it is.
Albert Yu Cheong LAI