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The high temperatures (in degrees Fahrenheit) of a random sample of 48 small towns are given below:

[tex]
\[
\begin{array}{|r|r|r|r|}
\hline
99.6 & 99.9 & 96.8 & 96.9 \\
\hline
96.3 & 98.3 & 99.1 & 97.6 \\
\hline
97.7 & 96.5 & 97.5 & 99.7 \\
\hline
96.7 & 98.7 & 99.2 & 97.1 \\
\hline
98.3 & 99.3 & 98.5 & 97.2 \\
\hline
99.6 & 96.4 & 98.7 & 98.1 \\
\hline
98.9 & 98.6 & 96.4 & 99.8 \\
\hline
99.9 & 98.1 & 98.4 & 98.5 \\
\hline
99.7 & 99.1 & 97.3 & 96.9 \\
\hline
97.3 & 97.4 & 97.8 & 96.7 \\
\hline
99.3 & 97.7 & 99.4 & 98.4 \\
\hline
98.0 & 97.0 & 98.8 & 98.0 \\
\hline
\end{array}
\]
[/tex]

Assume that high temperatures are normally distributed. Based on this data, find the 95% confidence interval of the mean high temperature of towns. Enter your answer as an open interval (i.e., parentheses with a comma) accurate to two decimal places (because the sample data are reported accurate to one decimal place).

95% C.I. = ( )

Note: The answer should be obtained without any preliminary rounding. However, the critical value may be rounded to 3 decimal places.

Answer :

To find the 95% confidence interval for the mean high temperature of the small towns, we follow these steps:

1. Collect the Data: We start with the high temperatures provided for 48 small towns.

2. Calculate the Sample Mean: The sample mean [tex]\(\bar{x}\)[/tex] is the average of all the temperature values. From the data, the sample mean is 98.15°F.

3. Calculate the Sample Standard Deviation: The sample standard deviation [tex]\(s\)[/tex] gives us a measure of the spread of the temperatures around the mean. For this data set, the sample standard deviation is 1.08°F. This calculation uses Bessel's correction, which means dividing by the sample size minus one ([tex]\(n-1\)[/tex]) for an unbiased estimate.

4. Determine the Sample Size: The number of temperatures in our sample is 48, so [tex]\(n = 48\)[/tex].

5. Determine the Confidence Level: We're asked for a 95% confidence interval, so the confidence level is 95%.

6. Find the Critical t-Value: Since the high temperatures are assumed to be normally distributed and the sample size is less than 30, we use the t-distribution. The critical t-value for a 95% confidence level with [tex]\(n - 1 = 47\)[/tex] degrees of freedom is approximately 2.012.

7. Calculate the Margin of Error: The margin of error (ME) is calculated using the formula:
[tex]\[
\text{Margin of Error} = t \times \left(\frac{s}{\sqrt{n}}\right)
\][/tex]
Plugging in the values, we get:
[tex]\[
\text{Margin of Error} = 2.012 \times \left(\frac{1.08}{\sqrt{48}}\right) \approx 0.31
\][/tex]

8. Calculate the Confidence Interval: The confidence interval (CI) is given by:
[tex]\[
\text{CI} = (\bar{x} - \text{ME}, \bar{x} + \text{ME})
\][/tex]
[tex]\[
\text{CI} = (98.15 - 0.31, 98.15 + 0.31) = (97.84, 98.46)
\][/tex]

Therefore, the 95% confidence interval for the mean high temperature of these small towns is [tex]\((97.84, 98.46)\)[/tex].

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Rewritten by : Jeany