A sample of 60 diaphragm valves, used in the control system of a chemical process, are placed on life test without replacement. The first 9 failures are observed after

\(\begin{array}{lllllllll}3.6 & 6.9 & 9.5 & 15.7 & 27.3 & 41.2 & 81.7 & 178.3 & 227.1\end{array}\)

hours. Using the Weibull model, estimate the mean life of this valve. How does this value compare with the mean life that would have been obtained under the exponential assumption?