John is throwing a dart at a dartboard. There are 4 rings that surround the bull's-eye ring,
which is located at the center of the dartboard.
The radius of the bulleyes region is 1 cm. The
radius of the first ring surrounding the bulleyes
is 2 cm more than that of the bulleyes and
the radius of every ring after that is 1 cm
more than that of the preceding ring. What is
the probability of John getting a dart on the
bulleyes if he cannot miss the darboard but is
randomly aiming at it?