The computational time of a statistical analysis applied to a data set can sometimes increase with the square of N, the number of rows of data. Suppose that for a particular algorithm, the computation time is approximately T = 0.004N² seconds. Although the number of rows is a discrete measurement, assume that the distribution of N over a number of data sets can be approximated with an exponential distribution with a mean of 10,000 rows. Determine the probability density function and the mean of T .