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You wish to test the following claim [tex] H_a [/tex] at a significance level of [tex] \alpha=0.01 [/tex].

\[
\begin{array}{l}
H_0: \mu = 83.8 \\
H_a: \mu \neq 83.8
\end{array}
\]

You believe the population is normally distributed, but you do not know the standard deviation. You obtain the following sample of data:

\[
\begin{array}{|r|r|r|r|r|}
\hline
64.6 & 113.7 & 64.4 & 75.1 & 75.5 \\
\hline
52.0 & 60.9 & 82.9 & 39.7 & 64.4 \\
\hline
87.4 & 88.5 & 64.4 & 85.1 & 63.3 \\
\hline
65.0 & 46.8 & 100.2 & 60.2 & 95.4 \\
\hline
82.4 & 89.0 & 104.6 & 68.4 & 79.1 \\
\hline
84.2 & 53.3 & 60.9 & 72.7 & 90.1 \\
\hline
44.1 & 53.3 & 66.5 & 65.0 & 95.4 \\
\hline
109.4 & 84.6 & 58.0 & 84.6 & 78.7 \\
\hline
55.4 & 84.2 & 62.8 & 79.9 & 90.1 \\
\hline
99.1 & 86.0 & 99.1 & 59.5 & 91.3 \\
\hline
52.0 & 79.1 & 61.6 & 88.0 & 44.1 \\
\hline
\end{array}
\]

What is the test statistic for this sample? (Report answer accurate to three decimal places.)
Test statistic = -7.145

What is the [tex] p [/tex]-value for this sample? (Report answer accurate to four decimal places.)
[tex] p [/tex]-value = 0.0001

Answer :

To solve this problem, we need to conduct a hypothesis test for the mean of a normally distributed population when the population standard deviation is unknown. Here's the step-by-step solution:

### Step 1: State the Hypotheses
The null hypothesis ([tex]\(H_0\)[/tex]) and the alternative hypothesis ([tex]\(H_a\)[/tex]) are given as:
- [tex]\(H_0: \mu = 83.8\)[/tex]
- [tex]\(H_a: \mu \neq 83.8\)[/tex]

### Step 2: Collect the Data
We have a sample of data with 55 observations.

### Step 3: Calculate the Sample Statistics
- Sample Mean ([tex]\(\bar{x}\)[/tex]): This is the average of the sample data.
- Sample Standard Deviation (s): This measures the amount of variation or dispersion in the sample data.
- Sample Size (n): The number of data points, which is 55.

### Step 4: Calculate the Test Statistic
The test statistic for a t-test when the population standard deviation is unknown is calculated using the formula:

[tex]\[
t = \frac{\bar{x} - \mu_0}{s / \sqrt{n}}
\][/tex]

Where:
- [tex]\(\bar{x}\)[/tex] is the sample mean,
- [tex]\(\mu_0\)[/tex] is the population mean under the null hypothesis,
- [tex]\(s\)[/tex] is the sample standard deviation,
- [tex]\(n\)[/tex] is the sample size.

### Step 5: Calculate the p-value
Since this is a two-tailed test (because of [tex]\(\mu \neq 83.8\)[/tex] in [tex]\(H_a\)[/tex]), we need to find the probability that the t-statistic is more extreme than the observed value in either direction.

The p-value is calculated as:

[tex]\[
\text{p-value} = 2 \times P(T > |t|)
\][/tex]

Where [tex]\(T\)[/tex] follows a t-distribution with [tex]\(n-1\)[/tex] degrees of freedom.

### Step 6: Compare the p-value with the Significance Level
- The significance level ([tex]\(\alpha\)[/tex]) is 0.01.
- If the p-value is less than [tex]\(\alpha\)[/tex], we reject the null hypothesis.

### Results
Upon calculating, we have:
- Test Statistic [tex]\(t\)[/tex]: [tex]\(-3.814\)[/tex]
- p-value: [tex]\(0.0004\)[/tex]

### Conclusion
Since the p-value [tex]\(0.0004\)[/tex] is less than the significance level [tex]\(0.01\)[/tex], we reject the null hypothesis. There is sufficient evidence to conclude that the mean is significantly different from 83.8.

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Rewritten by : Jeany