Final answer:
The slope of the least-squares regression line for Old Faithful eruptions represents the estimated increase in the time interval between eruptions for each minute of increase in eruption duration.
Step-by-step explanation:
The slope of the least-squares regression line represents the rate of change between the two variables displayed on a scatter plot. In the context of Old Faithful's eruptions, the slope of the line would indicate how much the time interval between eruptions increases (or decreases) for each additional minute of eruption duration based on the sample data. By knowing the duration of the previous eruption and using the slope, we can predict the estimated interval before the next eruption.
For example, if the slope is 10, that would mean for each additional minute that an eruption lasts, the time interval until the next eruption increases by an estimated 10 minutes, according to the least-squares regression model. However, it is important to note that such predictions are only estimates and may not always be perfectly accurate because real-life data often have variability that cannot be perfectly captured by a simple linear relationship.