Final answer:
Weekly sales data collected over twenty weeks is a true example of time-series data, which is used to observe trends, patterns, and changes over time.
Step-by-step explanation:
Sales data measured each week for the past twenty weeks are indeed examples of time-series data. Time series data are data points collected or recorded at specific intervals over time. This type of data is used to track changes, trends, or patterns within the data set as time progresses. When such data is graphically represented, such as in a time series graph, it allows for easy identification of any trends or patterns that may exist.
For instance, if a researcher wanted to analyze the sales performance of a store over twenty weeks, a time series graph would help visualize whether sales are increasing, decreasing, or remaining stable as the weeks go by. In business, time series analysis is crucial for understanding seasonal effects, cyclical patterns, and for making forecasts.