Instruction 3-3
the Stem-And-Leaf Display Below Represents the Number of Vitamin

Instruction 3-3
The stem-and-leaf display below represents the number of vitamin supplements sold by a health food store in a sample of 16 days.
$$\begin{array} { | l | l | } \hline \text { Stem } & \text { Leaves } \\\hline \text { 1H } & 99 \\\hline \text { 2L } & 0023 \\\hline \text { 2H } & 567 \\\hline \text { 3L } & 034 \\\hline \text { 3H } & 568 \\\hline \text { 4L } & 1 \\\hline\end{array}$$ Note (1): 1H means the "high teens" = 15, 16, 17, 18, or 19; 2L means the "low twenties" = 20, 21, 22, 23, or 24; 2H means the "high twenties" = 25, 26, 27, 28, or 29, etc.
Note (2): For this sample, the sum of the observations is 448, the sum of the squares of the observations is 13,356, and the sum of the squared differences between each observation and the mean is 812.
-Referring to Instruction 3-3,the interquartile range of the number of vitamin supplements sold in this sample is_____________ .