Determine the IQR of this data then indicate whether the data set contains any outliers . Explain how you determined this

Place the values in ascending order first:

4, 10, 10, 11, 12, 12, 12, 12, 13, 13, 15, 15, 17, 18, 19, 20

There are 16 values

IQR is 3/4th term - 1/4th term

The 12th value is 15 while the 4th value is 11

Therefore IQR = 15-11 which is 4

I would say the outlier is 4.

Justification: Figure out the mean with the value of 4 then discount it to see whether the mean is affected by the outlier.

Yes, two vertical lines can be complementary