Question 43936
First, rearrange them in ascending order, so that
13,7,15,13,13,12,9,11,19,9
becomes
7, 9, 9, 11, 12, 13, 13, 13, 15, 19
The 1st and 3rd quartiles are the middle values of the left and right-hand halves of the data, respectively.
That would be 9 and 13.