\( \definecolor{colordef}{RGB}{249,49,84} \definecolor{colorprop}{RGB}{18,102,241} \)
The following data shows the marks (out of 20) obtained by 9 students in a math exam: $$1,\ 19,\ 10,\ 2,\ 18,\ 11,\ 5,\ 15,\ 10$$Find the interquartile range of the marks.