A salesman carries $3$ bags with $30$ balls in each of them. A bag can carry maximum of $30$ balls. He goes to the city to sell the ball but before entering the city he has to cross 30 tax stations, where he has to pay one ball from each bag as "tax". How many balls will he have at the end?
Best I could come up with was $25$. Is there any better answer? Is $25$ mathematically best possible?
Does this question even belong here? Or should I move it to puzzling?