IBM三月

constant

Consider 3 points chosen at random in an unit square. These points form a triangle. We want to compute the expected (average) area of this triangle. This can be done by answering the following questions.

1. Consider the minimum rectangle (with edges parallel to the edges of the unit square), R, containing the 3 random points. On average what is the area of R?

2. Given R, there are two configurations of the three points
which occur with positive probability. They are Case A - 2 points at opposite corners of R, remaining point in the
interior of R.www.ddhw.com

Case B - 1 point at a corner of R, 1 point along each of the 2 edges of R opposite the corner.

Show that the probabilities of occurrence of these two cases are independent of R. What are these probabilities?

3. What is the expected fraction of the area of R which is inside the triangle for each of the cases A and B above?

4. Combining the answers to questions 1-3, what is the expected area of the triangle formed by three points chosen at random in an unit square?

www.ddhw.com

 

constant

  我算得11/144。还有谁算了？