The interquartile range = 6.25
Explanation:The given dataset is:
11, 11.5, 10.5, 17, 14.5, 14.5, 18, 17, 19
Rearrange the data in ascending order
10.5, 11, 11.5, 14.5, 14.5, 17, 17, 18, 19
The number of terms in the data, N = 9
The lower quartile is calculated as:
[tex]\begin{gathered} Q_1=(\frac{N+1}{4})^{th}term \\ \\ Q_1=\frac{9+1}{4}^{th}term \\ \\ Q_1=2.5th\text{ term} \\ \\ Q_1=\frac{11+11.5}{2} \\ \\ Q_1=\frac{22.5}{2} \\ \\ Q_1=11.25 \end{gathered}[/tex]The upper quartile is calculated as:
[tex]\begin{gathered} Q_3=(\frac{3(N+1)}{4})^{th\text{ }}term \\ \\ Q_3=\frac{3(9+1)}{4}th\text{ terms} \\ \\ Q_3=7.5th\text{ term} \\ \\ Q_3=\frac{17+18}{2} \\ \\ Q_3=17.5 \end{gathered}[/tex]The interquartile range = Upper quartile - Lower quartile
The interquartile range = 17.5 - 11.25
The interquartile range = 6.25