Traditionally, the free space is stuck in the center of the card, and thus it can be ignored for the purposes of the problem.  The right answer is 24!<p>Incidentally, if you're trying to explain the results of this calculation to a middle school English teacher, I recommend "More than there are grains of sand on a beach."  It relaxes the worry they really have and is non-specific enough to avoid sounding threatening.  (Ask me no questions I'll tell you no lies.)