[Spivak]

The time it takes for your function to complete is now a continuous random variable X + r where r is the real time it take for your function to complete.

    E(X + r) = E(X) + E(r) = E(X) + r

    E(X + r) is the sample mean which is easy to calculate
    
    E(X) = 1/2 * (max(sample) - min(sample))