Results from testing for the presence of a pollutant in a local stream have hist

Question

Results from testing for the presence of a pollutant in a local stream have historically had a mean of 10 mg/liter and a standard deviation of 2 mg/liter. Six recent tests collected from the stream have the following values: 12.7, 15.1, 9.5, 13.7, 19.6, 16.4 mg/liter. Has the recent pollutant level exceeded the historical value of 10 mg/liter? Clearly state your null and alternative hypotheses, your chosen significance level, and your conclusion.

Explanation / Answer

Use the Z-table process. Given the data you can determine the calculate the sample mean. Null: mu=10, Alt: mu>10 with alpha=.01 using the equation z=(sample mean-mean)/(standard deviation/square root of sample size) you then compare it to the actual Z value. You find the actual Z value by using alpha and using the tables in your book. When you compare the two you can determine whether you keep your null or not.

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