Part 1

Dissolved oxygen (DO) is the most critical indicator of a lake's health and water quality. For a healthy game-fish population, oxygen levels in the 6-10 mg/L range are necessary. Respiration stress in most fish occurs when oxygen levels are reduced to 3-4 mg/L. At a popular fishing lake, a study was performed of the oxygen levels. 18 Random samples were taken over a 30 day period. The average of the 18 samples was 7.6 with a standard deviation of 0.66. 1a) What is the standard error of the means, ???, for the distribution where n= 18 and the population standard deviation is estimated with s? (take out to 4 decimal places) 1b) What is the 95% confidence interval for the true value of the DO level? 1c) Test the hypothesis that the true average of the DO is 8 mg/L (two-tailed test). What is the p value? (use closest t value from table to determine.) 1d) At a 95% confidence level, would you reject the null hypothesis?

O 8+ 2.110 0.66 O 8 + 2.110 0.66 V17 O 7.6 + 2.110 0.66 O 7.6 + 2.110 0.66 17 O 8 + 1.740 0.66 O 7.6 + 1.740 0.66