Your initial data is:
8, 9, 9, 9, 6, 9 , 8, 6, 8, 6, 8 , 8, 8, 6, 6, 6, 3, 8, 8, 9
To find the minimum, Lower quartile, Medina, Upper quartil, Maximun, and the interquertile range, we need to organize the data as:
3 , 6, 6, 6, 6, 6, 6, 8, 8, 8,
1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th
8, 8, 8, 8, 8, 9, 9, 9, 9, 9
11th 12th 13th 14th 15th 16th 17th 18th 19th 20th
Now, the minimum value is 3
The maximum value is 9
The position of the lower quartile is equal to:
Pos Q1 = (n+1)/4 = (20+1)/4 = 5.25
So, the value at position 5th and 6th is 6. It means that the lower quartile is 6.
At the same way the position of the median and the upper quartile are:
Pos Median = (n+1)/2 = 21/2 = 11.5
It means that the median is 8.
Pos Q3 = 3(n+1)/4 = 3*21/4 = 15.75
In this case the value at position 15th is 8 and the value at position 16th is 9. So, the upper quartile is 8.5
Finally, the IQR can be calculated as:
IQR = Q3 - Q1
IQR = 8.5 - 6 = 2.5
Answer: MInimum: 3
Q1 = 6
Median: 8
Q3 = 8.5
Maximum = 9
IQR = 2.5