91影视

Data for $12$ subjects are summarized as $251卤45$ (in milliseconds). To Find the sample standard deviation $s_x$ for these measurements.

The standard deviation is divided by the square root of the sample size to get the standard error of the mean.

Standard error of mean is $\stackrel{炉}{E}=\frac{s_x}{\sqrt{n}}$, and multiply with $\sqrt{n}$on both sides.

Then, $s=\stackrel{炉}{E}脳\sqrt{n}$.

where, Sample size $n$is $12$, Standard error of mean $\stackrel{炉}{E}=45$, and the population mean $\stackrel{炉}{x}$is$251$.
localid="1650092899445" $$\begin{gathered} s=\stackrel{炉}{E}脳\sqrt{n} \\ =45脳\sqrt{12} \\ =155.8846 \end{gathered}$$
Therefore, the standard deviation is localid="1649913384538" $155.8846$.

To explain why the provided interval $251卤45$ is not a confidence interval.

The confidence interval is calculated by using the formula$=\stackrel{炉}{x}卤\left(t^{*}脳\stackrel{炉}{E}\right)$.

The interval in the problem is $\stackrel{炉}{x}卤\stackrel{炉}{E}$.

And, $t^{*}$is unknown.

As a result, the provided interval is not a confidence interval.