+476 
My Work:
Okay so the IQR is the range of the middle half of the data set, or the difference between the third and first quartiles.
I lined up the numbers from least to greatest:
10, 12, 14, 15, 15.5, 16, 17.5, 18, 19
Then I found the first and third quartiles.
Min Q1 Q2 Q3 Max
10, 12, 14, 15, 15.5, 16, 17.5, 18, 19
So then I did 17.5 - 14 = 3.5 This doesn't match any of the choices above.
+129847 10 12 14 15 15.5 16 17.5 18 19
Q2 = 15.5
Q1 = [12 + 14] / 2 = 26 / 2 = 13
Q3 = [ 17.5 + 18 ] / 2 = 17.75
So....the IQR is just 17.75 - 13 = 4.75
+476 Can you tell me why those numbers had to be added so I know for future questions like this?
+129847 We are actually finding 3 medians
The first is the median of the data set = 15.5 = Q2
Then....we look at the four data points to the left of Q2
These are 10 12 14 15
The median of these = [ 12 + 14]/2 = 13 = Q1
And then we do the same thing with the four data points to the right of Q2
These are 16 17.5 18 19
The median of these = [ 17.5 + 18 ] / 2 = 17.75 = Q3
So....the IQR = Q3 - Q1 = 4.5
Hope that helps
