GRE数学考点：Geometric Figures

　　Geometric Figures

　　If a point is selected at random inside a geometric figure, then the
probability that the selected point lies inside a particular region is the ratio
of their areas:

　　area of the particular region inside the figure/area of the whole
figure.

　　Example:

　　The probability that a randomly selected point within the square lies
inside the circle=area of circle/area of square=∏r2/(4r2)= ∏/4.

　　Remember:

　　If the particular region is not completely inside the figure, then use only
the area that is inside the figure.