A line of best fit shows the overall trend through scattered measurements. To interpret its slope, choose two readable points on the line, then divide the vertical change by the horizontal change. Slope gives the predicted output change for one more input unit. Individual dots can miss the line, so using two dots may give the wrong rate.
Hints
- Hint 1
A line of best fit models the trend rather than passing through every measured dot. Choose two points on the drawn line whose coordinates you can read from the axes. Which points are easiest to use?
- Hint 2
The slope compares change in ink to change in posters. Put the ink change on top and the poster change on the bottom, subtracting the two points in the same order. What are the rate’s units?
Step-by-step
Read and interpret the fitted line’s slope
Step 1Read two points on the fitted line
The drawn line of best fit passes through and . Read those coordinates from the axis labels. Use points on the line rather than two black dots: the dots are individual print runs, while the line represents the overall trend.
- Step 2
Set up the rate in the right order
Slope means vertical change divided by horizontal change. Ink is measured vertically and posters horizontally, so this rate has milliliters per poster. Using the line points in the same order on top and bottom gives . Reversing the fraction would answer a different question: posters per milliliter.
- Step 3
Calculate and interpret the slope
Type in Desmos. It prints . So the line of best fit predicts about additional milliliters of ink for each additional poster printed. This describes a change, not the ink used when zero posters are printed. Choice A.