To find the mean of the data set, we use the formula:
\[
\mu = \frac{\sum_{i=1}^N x_i}{N}
\]
where \( N \) is the number of observations and \( x_i \) are the individual data points. For our data set:
\[
\text{Data} = [8, 10, 11, 11, 8, 7, 7, 9, 7, 7, 9, 7, 8]
\]
Calculating the sum of the data:
\[
\sum_{i=1}^{13} x_i = 8 + 10 + 11 + 11 + 8 + 7 + 7 + 9 + 7 + 7 + 9 + 7 + 8 = 109
\]
Now, substituting into the mean formula:
\[
\mu = \frac{109}{13} = 8.4
\]
To find the median, we first sort the data:
\[
\text{Sorted Data} = [7, 7, 7, 7, 8, 8, 9, 9, 10, 11, 11]
\]
Since there are 13 observations (an odd number), the median is the middle value, which is the 7th value in the sorted list:
\[
\text{Median} = 9
\]
The mode is the value that appears most frequently in the data set. In our data:
\[
\text{Frequencies: } 7 \text{ appears } 4 \text{ times, } 8 \text{ appears } 3 \text{ times, } 9 \text{ appears } 2 \text{ times, } 10 \text{ appears } 1 \text{ time, } 11 \text{ appears } 2 \text{ times.}
\]
Thus, the mode is:
\[
\text{Mode} = 7
\]
The mean is \( \mu = 8.4 \), the median is \( 9 \), and the mode is \( 7 \).
\[
\boxed{\text{Mean: } 8.4, \text{ Median: } 9, \text{ Mode: } 7}
\]