In 20122012, the mean zinc concentration in a lake was reported as 0.0350.035 mg/L\text{mg/L}. In 20212021, a random sample of 99 measurements yielded: 0.0320.032, 0.0340.034, 0.0360.036, 0.0330.033, 0.0350.035, 0.0370.037, 0.0340.034, 0.0360.036, 0.0330.033 mg/L\text{mg/L}. Assume normality and no outliers. At the α=0.05 \alpha = 0.05 significance level, is there evidence that the mean zinc concentration has changed since 20122012?

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Problem 53Multiple Choice

In $2012$ , the mean zinc concentration in a lake was reported as $0.035$ $mg/L$ . In $2021$ , a random sample of $9$ measurements yielded: $0.032$ , $0.034$ , $0.036$ , $0.033$ , $0.035$ , $0.037$ , $0.034$ , $0.036$ , $0.033$ $mg/L$ . Assume normality and no outliers. At the $alpha equals 0.05$ significance level, is there evidence that the mean zinc concentration has changed since $2012$ ?

There is sufficient evidence to conclude that the mean zinc concentration has changed since $2012$

The sample mean equals the historical mean, so no test is needed

There is insufficient evidence to conclude that the mean zinc concentration has changed since $2012$

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