Recall that the upper quartile, or third quartile, is the value under which 75% of data points are found when arranged in increasing order.
Therefore, to determine the third quartile, we have to order the given data from lowest to highest:
[tex]2,3,4,6,7,8,9,9,9,10,13,15,18.[/tex]Therefore:
[tex]Q_3=\frac{10+13}{2}=\frac{23}{2}=11.5.[/tex]Answer: Option E.
