the interquartile range is the Q3-Q1 where Q3 is 75th percentile and Q1 is the 25th percentile.
so the total count is 20 so 25 percentile is 25% of 20 =5 and 75th percentile is 75% of 20 = 15 and since the number are already arranged in order we just pick the 15th number-5th number thus, our answer is
