Rescued from a corrupted hard drive by: David Morgan-Mar
The author writes:
How many tennis balls must there be?
If you take the number of people who play tennis, and assume they open a new can of balls on average once every 10 matches (I'm combining pros who go through, what, a hundred balls a match, and rank amateurs who play with the same balls until they wear out completely), and multiply up the numbers, you get something like eleventy trillion tennis balls! Which would form a sphere the size of the moon!
Where are they all going???