8. The failure behavior of a downhole equipment is given by a Weibull distribution with scale parameter 2.8 years and shape factor 1.6. When will 90% of the equipment need to be replaced? 9. Given the following permeability values: k (mD)=(40.5, 49.5, 70, 90, 110, 141, 182, 245, 405), (a) fit a log-normal distribution to the data using probability plotting and calculate the geometric parameters a and ß, (b) estimate the 95% confidence interval around the geometric mean.