The Environmental Protection Agency sets limits on the maximum allowable concentration of certain chemicals in drinking water. For the substance PCB, the limit was set at 5 ppm (parts per million). The PCB level is unsafe if it is greater than 5 ppm. A random sample of 36 water specimens from the same well results in a mean PCB concentration of 5.2 ppm with standard deviation of 0.6 ppm. Does the data substantiate that the water is unsafe?

The weibull distribution is widely used in statistical problems relating to aging of solid insulating materials subjected to aging and stress. use this distribution as a model for time (in hours) to failure of solid insulating specimens subjected to ac voltage. the values of the parameters depend on the voltage and temperature; suppose α = 2.5 and β = 190. (a) what is the probability that a specimen's lifetime is at most 250? less than 250? more than 300? (round your answers to four decimal places.) at most 250 less than 250 more than 300 (b) what is the probability that a specimen's lifetime is between 100 and 250? (round your answer to four decimal places.) (c) what value is such that exactly 50% of all specimens have lifetimes exceeding that value? (round your answer to three decimal places.) hr