Final answer:
An appropriate key for a stemplot is used to interpret the data displayed in the plot.
Step-by-step explanation:
An appropriate key for a stemplot is used to interpret the data displayed in the stem-and-leaf plot. It provides a guide to understanding the values represented in the plot. The stem represents the major digits of each data point, while the leaf represents the minor digits. The key typically includes the stems and the corresponding leaves, allowing one to read off the data values. For example, if the stem is 5 and the leaves are 1 and 2, the corresponding data values would be 51 and 52.