For a scatterplot with a drawn line of best fit, find the slope using two readable points on the line, not two data dots. Divide the change in the vertical value by the change in the horizontal value, then read both axis labels to state the rate in context. Don't confuse the line's starting value with its rate of change.
Hints
- Hint 1
The line of best fit gives predicted orders; the scattered dots show actual orders. Pick two points you can read on the line, even if neither point is a black dot.
- Hint 2
A slope is the change in the vertical value divided by the change in the horizontal value. Keep the two points in the same order when you subtract their coordinates.
- Hint 3
The horizontal axis measures spending in hundreds of dollars. If the slope gives orders per one horizontal unit, how many dollars does that unit represent?
Step-by-step
Read the fitted line and its units
Step 1Choose two points on the line
The line of best fit passes through and , so those points give its predicted orders at two spending amounts. Use points on the line, not two scattered dots: a dot shows an actual week's orders, which may differ from the prediction.
- Step 2
Set up the slope with the axis units
A slope is the change in the vertical value divided by the change in the horizontal value. Here that's . One horizontal unit means $100, not $1.
- Step 3
Calculate and interpret the rate
Type in Desmos. It shows : the line predicts 5 more orders per $100 increase in ad spending. The at zero spending is the intercept, or starting prediction, not the slope. Choice A.