The extra dollar was never missing. It just appeard to be missing in the way the problem was stated.
The room is $25 or $8.33 per person. They tip the bellboy $2 or $.66 per person. This makes the total paid per person $9.00. Then they each get 1 extra dollar back for a total of $10.00 per person.
This is CABL.com posting #153830. Tiny Link: cabl.co/mObi