A drawn line of best fit gives predicted values; the dots show measured values. For an average rate of change, read the line’s heights at the specified inputs, then divide the change in predicted heart rate by the change in training time. Type that quotient in Desmos. A falling line gives a negative rate, while using nearby dots can change its size.
Hints
- Hint 1
A line of best fit predicts heart rates; each dot records one runner’s measured heart rate. At each requested training time, read the line’s height, even if a dot is nearby. What two heights do you get?
- Hint 2
An average rate of change is the change in output divided by the change in input. Subtract the predicted heart rates in the same order as the training times. Should the result be positive or negative for a falling line?
Step-by-step
Read the fitted line and find its rate
Step 1Read the two predictions
The line of best fit gives the predicted heart rate. At , the line is at ; at , it’s at . So use and . Read the line, not the nearby dots, for predicted values.
- Step 2
Write the rate using both changes
The average rate of change is the change in predicted heart rate divided by the change in training time. Go from the first point to the second in both subtractions:
- Step 3
Calculate and interpret the rate
Type in Desmos. It shows . So the line predicts a decrease of beat per minute in resting heart rate for each additional minute of training. Choice A.