Geometric probability refers to the probability of an area
            rather than a number.  Geometric probability compares the size of the favorable area to
            the total area.  It is usually written as a fraction, however it can also be given as a
            decimal or percent.
Suppose a rectangular pool is
            surrounded by a deck and a fence.  The pool is 30 ft long and 15 ft wide.  The deck is a
            consistent width around the pool.  If a baseball is hit into the fenced area, what is
            the probability that the baseball will land in the
            pool?
Allow x to represent the width of the
            deck.
The favorable area is the area of the pool.  30 * 15
            = 450 sq ft
The total area is the area of the pool plus the
            additional area of the deck.
total length as a binomial: 
            30 + x + x = 2x + 30
total width as a binomial:  15 + x + x
            = 2x + 15
total area:  (2x + 30)(2x + 15) = 4x^2 + 90x +
            450
The geometric probability of the ball landing in the
            pool is:
450 / (4x^2 + 90x +
            450)
If you know the width of the deck, you can get a
            numerical answer.  For example, if the deck is 6 ft
            wide...
450 / (4 * 6^2 + 90 * 6 +
            450)
450 / 1134 `~~` 0.3968 or about
            40%.
I hope this helped.
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