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3. + 0/1 points Previous Answers WackerlyStat7 8.E.088. RMy Notes + Ask Your Teacher The Environmental Protection Agency is concerned with the problem of setting criteria for the amounts of certain toxic chemicals to be allowed in freshwater lakes and rivers. A common measure of toxicity for any pollutant is the concentration of the pollutant that will kill half of the test species in a given amount of time (usually 96 hours for fish species). This measure is called LC50 (lethal concentration killing 50% of the test species). In many studies, the values contained in the natural logarithm of LC50 measurements are normally distributed, and, hence, the analysis is based on In(LC50) data. The Environmental Protection Agency (EPA) has collected data on LC50 measurements (concentrations that kill 50% of test animals) for certain chemicals likely to be found in freshwater rivers and lakes. For certain species of fish, the LC50 measurements (in parts per million) for DDT in 12 experiments were as follows. 18, 6, 22, 20, 12, 5, 9, 4, 9, 1, 3, 9 Estimate the true mean LC50 for DDT with confidence coefficient 0.90. Assume that the LC50 measurements have an approximately normal distribution. (Round your answers to three decimal places.) x ppm, x ppm) You may need to use the appropriate appendix table or technology to answer this question. Submit Answer

Answer 1

Using Minitab instructions to construct the confidence interval: • • Enter the data in Minitab sheet Choose Stat > Basic Statistics >1-Sample t From the drop-down list, select one or more sample, own column. Shift the variable C3 Choose options confidence level as 90.0 alternative hypothesis (6) Click OK • The output is, One-Sample T: C1 Variable ci N Mean StDev SE Mean 12 9.836.89 1.99 90% CI (6.258, 13.402) The 90% confidence interval for true mean LC50 for DDT is, 6.258 and 13.402.