1/9998 is
  1/(10000-2) is
  (1/10000) / (1 - 2/10000)

which is an infinite sum of geometric progression with an initial value of 1/10000 and ratio of 2/10000. In other words,

  x1 = 1/10000;            //  0.0001
  x2 = x1 + x1 * 2/10000;  //  0.0001 0002
  x3 = x2 + x2 * 2/10000;  //  0.0001 0002 0004 0008
  ...

Magic

  O_O

[0] http://en.wikipedia.org/wiki/Geometric_progression