Find the interquartile range given these data points: 57,66,69,71,72,73,74,77,78,7879,79,81,81,82,83,83,88,89,94.

Question

When I used the TI-84 calculator, I got ...
Q1=72.5
Q3=82.5

IQR=Q3-Q1=82.5-72.5=10

But..

When I created a stem and leaf plot I found that
Q2= (78+79)/2 =78.5

Q1=72
Q3=83

IQR= 83-72=11

So is it 10 or 11?

Did I do something wrong when using the stem and leaf plot?

Answer 1

There are 20 data in total.
Q1 should be (5th datum + 6th datum)/2
Q2 should be (10th datum + 11th datum)/2
Q3 should be (15th datum +16th datum)/2

Your own calculation is wrong.
Calculate yourself again.

(Ans: IQR=10)