A line of best fit predicts a height from the overall pattern, while a plotted dot shows a height actually measured. To find the difference, compare the dot and line at the same , then subtract their heights. A nearby dot cannot stand in for the line’s prediction.
Hints
- Hint 1
A data point is one actual measurement. Follow the vertical gridline above the requested amount of fertilizer to the dot. What height does the dot show?
- Hint 2
The prediction comes from the line of best fit. At the same amount of fertilizer, read where the line crosses that vertical gridline, even if a dot sits higher or lower.
- Hint 3
The residual is measured height minus predicted height. Subtract the line’s height from the dot’s height at the same to find the vertical difference.
Step-by-step
Read the dot and the line
Step 1Read the measured height
No Desmos needed. Read the dot and the drawn line directly from the scatterplot. At , the dot is about , so the observed height, meaning the measured height, is about cm.
- Step 2
Read the predicted height
Stay at and look where the line of best fit crosses. It is above the -cm gridline, at about cm. That is the predicted height; a nearby dot would be another measurement.
- Step 3
Find the difference
Subtract the predicted height from the observed height to get the residual:
The plant is about cm taller than predicted. Choice B.