236. A certain hotelkeeper was never at a loss to produce a large
appearance with small means. In the dining-room were three tables,
between which he could divide 21 bottles of wine, of which 7 only
were full, 7 half-full, and 7 apparently just emptied, and in such a
manner that each table had the same number of bottles and the same
quantity of wine. How did he manage it?