Step 1: Definition of the median

             Median:

                    The median of a set of data is the middlemost number in the set.

                    The median is also the number that is halfway into the set.

•   If there is an odd number of observations, the median is the middle value.

                  let's say n is the number of observations

                          If n is odd, The median = \frac{n+1}{2}th term

•   If there is an even number of observations, the median is the average of the two middle values.

                      If n is even, The median = \frac{\frac{n}{2}+\left(\frac{n}{2}+1\right)}{2}  

Step 2: Arrange the data in either ascending order or descending order

            GIVEN: 9, 6, 12, 5, 17, 3, 9, 5, 10, 2, 8, 7

            Ascending order

                      2, 3, 5, 5, 6, 7, 8, 9, 9, 10, 12, 17

Step 3: Count the number of observations and find the median of the given data

            There are 12 observations

                n = 7 is a even number

        There is an even number of numbers, so there are two numbers in the middle.

        The median is the mean of the two middle numbers.

            So, the median = \frac{\frac{n}{2}+\left(\frac{n}{2}+1\right)}{2}=\frac{\frac{12}{2}+\left(\frac{12}{2}+1\right)}{2}=\ \frac{6^{th}\ term+\ 7^{th}\ \ term}{2}

                    Median = \frac{7 + 8}{2}

                                  = \frac{15}{2}

                    Hence, the median = 7.5