The average level of dissolved oxygen in a stream or river is an important indicator of the water's ability to support aquatic life. A researcher measures the DO level at 43 randomly chosen locations along a stream. Below are the results in mg/l:

3.84	4.08	4.24	5.39	4.04
5.7	5.06	4.94	2.21	6.03
5.83	4.3	4.06	3.23	4.94
4.6	2.67	5.12	6.75	3.08
2.98	4.89	4.68	4.52	5.9
2.5	4.12	5.89	4.1	2.98
5.3	3.64	4.43	4.85	3.48
3.06	3.59	3.51	4.89	4.15
4.34	4.22	1.77

An average level of dissolved oxygen less than 4.8 mg/l puts aquatic life at risk. At 5% significance level can we conclude that an average level of dissolved oxygen different from 4.8 mg/l? (Note: The average and the standard deviation of the data are respectively 4.28 mg/l and 1.1 mg/l.)

Procedure: Select an answer One mean Z Hypothesis Test One proportion Z Hypothesis Test One variance χ² Hypothesis Test One mean T Hypothesis Test

Assumptions: (select everything that applies)

Step 1. Hypotheses Set-Up:

$\displaystyle {H}_{{0}}:$  Select an answer p σ² μ =	, where Select an answer μ σ² p is the Select an answer population variance population proportion population mean and the units are Select an answer kg/l mg/l DO lbs/gal
$\displaystyle {H}_{{a}}:$ Select an answer μ σ² p ? ≠ < >	, and the test is Select an answer Right-Tail Two-Tail Left-Tail

Step 2. The significance level $\displaystyle \alpha=$ %

Step 3. Compute the value of the test statistic: Select an answer z₀ f₀ t₀ χ²₀ = (Round the answer to 3 decimal places)

Step 4. Testing Procedure: (Round the answers to 3 decimal places)

CVA	PVA
Provide the critical value(s) for the Rejection Region:	Compute the P-value of the test statistic:
left CV is and right CV is	P-value is

Step 5. Decision:

CVA	PVA
Is the test statistic in the rejection region?	Is the P-value less than the significance level?
? yes no	? no yes

Conclusion: Select an answer Do not reject the null hypothesis in favor of the alternative. Reject the null hypothesis in favor of the alternative.

Step 6. Interpretation:

At 5% significance level we Select an answer DO DO NOT have sufficient evidence to reject the null hypothesis in favor of the alternative hypothesis.