Chapter 8.3, Problem 80E

a)

To determine

To find sample standard deviation.

Answer to Problem 80E

The sample standard deviation is 155.8846 ms.

Explanation of Solution

Given:

  $\begin{array}{l}Standarderror=SE=45\hfill \\ Samplemean=\overline{x}=251\hfill \\ Samplesize=n=12\hfill \end{array}$

Formula:

Standard error:

  $SE=\frac{s_x}{\sqrt{n}}$

Calculation:

Using the formula,

  $\begin{array}{l}45=\frac{s_x}{\sqrt{12}}\\ s_x=45\times \sqrt{12}\\ s_x=155.8846\end{array}$

b)

To determine

To find the actual confidence level.

Answer to Problem 80E

The actual confidence level is 68%

Explanation of Solution

Given:

  $\begin{array}{l}Standarderror=SE=45\hfill \\ Samplemean=\overline{x}=251\hfill \\ \begin{array}{l}Samplesize=n=12\\ Criticalt*=1\end{array}\hfill \end{array}$

Calculation:

The critical value t*=1 assumed as it is one standard deviation.

The degrees of freedom =df = n-1= 12-1 = 1

Therefore, the confidence level can be found using excel formula,

=2*TDIST(1,11,2)

So, confidence level = 68%