Ok so here are the data elements:

16,18,21,23,24,25,25,26,27,29,31

My books says that these are the outliers :

16 and 31

BUT how can this be

Q1 = (11+1)*0.25= 3rd element

Third element = 21

Q3 = (11+1)*0.75= 9th element

Ninth element = 27

IQR = Q3 - Q1 = 6

SO OUTLIERS =

Q1 + 1.5 * IQR =

21 + 1.5 * 6 = 30?? There aren't 30 elements?

OR

Q3 - 1.5 * IQR =

27 - 1.5 * 6 = 18 ?? There aren't 18 elements?

Please Help! :S