3.9 Functions of random variables (derived distributions) Consider a square service region of unit area in which travel is rightangle and directions of travel are parallel to the sides of the square. Let (X_{1}, Y_{1}) be the location of a mobile unit and (X_{2}, Y_{2}) the location of a demand for service. The travel distance is D = D_{x} + D_{y} where D_{x} = X_{1}  X_{2} and D_{y} = Y_{1}  Y_{2} We assume that the two locations are independent and uniformly distributed over the square.
