On a scatterplot with a fitted straight line, “for each additional” asks for the slope: the predicted change in the vertical quantity for one unit of the horizontal quantity. Pick two readable points on the fitted line and divide the vertical change by the horizontal change. Using two measured dots instead can give a different rate because the line need not pass through them.
Hints
- Hint 1
The phrase “each additional minute” asks for a rate: the change in predicted fuel use for one more minute. On a straight line, that rate is its slope, not the fuel use at a particular time.
- Hint 2
Pick two readable points on the fitted line, not two scatterplot dots. The dots are measurements that may lie above or below the line. Which two points on the line have coordinates you can read?
- Hint 3
To find the slope, put the change in gallons over the change in minutes. Subtract the coordinates in the same order on top and bottom, then evaluate the fraction.
Step-by-step
Find the slope of the fitted line
Step 1Read two points on the line
The fitted line passes through and . These are points on the line, so they give its predicted fuel use; the scattered dots are measurements that can miss the line. Use points on the line, not two scatterplot dots, to find its slope.
- Step 2
Write the rate as a slope
“For each additional minute” asks for the slope, or change in gallons per minute. Put the change in gallons over the matching change in minutes, subtracting in the same order:
- Step 3
Calculate and interpret the rate
Type into Desmos. It shows , so the line predicts more gallons used for each additional minute of idling. Choice B.