1996 AIME Problem 12

For each permutation a_{1}, a_{2}, a_{3}, \ldots, a_{10} of the integers 1,2,3, \ldots, 10, form the sum

\left|a_{1}-a_{2}\right|+\left|a_{3}-a_{4}\right|+\left|a_{5}-a_{6}\right|+\left|a_{7}-a_{8}\right|+\left|a_{9}-a_{10}\right|

The average value of all such sums can be written in the form p / q, where p and q are relatively prime positive integers. Find p+q.