Hah, I remember having no clue what was going on the first time I read that, but it clicked just now. The fizzbuzz problem as described in that paragraph could almost be interpreted as 3 equations. The math was for something along the lines of this problem:

  x = fizz / 3
  x = buzz / 5
  x = (fizz * buzz) / 15

In this system of 3 equations, what is "x"?

Not sure what's going on with the 1-100 though.