91影视

Referring to Exercise 7 CQQ, it is given that a sample of size 12 is selected, showing the voltage level of smartphone batteries.

The number of values that can be considered independent in estimating a population parameter is called the degrees of freedom.

In other words, it is the value obtained by subtracting those number of parameters from the total number of values available that are used in the intermediate steps to compute the sample statistic.

Here, to construct the confidence interval of the mean value using the t distribution, the mean used to compute the interval is calculated from the sample values.

Thus, the sample mean (the parameter used in between the steps) is to be used to compute the confidence interval and is calculated from the available data.

Therefore, the degrees of freedom areas follows:

$$\begin{gathered} df=\text{Total}\text{number}\text{of}\text{values}-\text{Number}\text{of}\text{parameters} \\ =n-1 \\ =12-1 \\ =11 \end{gathered}$$

Thus, the value of the degrees of freedom is equal to 11.