The median of the numbers 3, 1, 1, 5, 2 and 7 is:

Median  is the value in a set which is most close to the middle of a range.

In other words, Median  is equal to  the middle value of a set of ordered data.

Given set of data is :

3,1,1,5,2,7

Firstly we will write it on order (ascending order)

1, 1, 2, 3, 5, 7

There are total 6 numbers (even)

We have a formula to find the position of median is  = 

$$\left(\frac{(n+1)}{2}\right)^{th}$$ term

Position of median  =

$$\frac{6+1}{2} = 3.5$$

Since there is an even number of observations in this data set, there is no longer a distinct middle value.

So, we take average of 3rd and 4th term

Median  = 

$$\frac{2+3}{2} = \frac{5}{2} = 2.5$$

So, median is 2.5