Question 13·Easy·Two-Variable Data: Models and Scatterplots
Each dot in the scatterplot above represents the number of minutes a student practiced piano and the number of measures the student could play correctly on one of twelve different days. The line of best fit for the data is also shown.
According to the line of best fit, about how many measures can a student be predicted to play correctly on a day when the student practiced for 30 minutes?
For prediction questions, always use the line of best fit: start at the given x-value, move to the line, then read the corresponding y-value. Use the gridlines to estimate carefully, and do not choose a value just because there is a data point near it.
Hints
Use the line, not the dots
The question says according to the line of best fit, so ignore individual points that are above or below the line.
Start at 30 on the x-axis
Find minutes on the horizontal axis and trace up to the line.
Read across to the y-axis
From the line, trace straight left or right to the y-axis and read the approximate number of measures.
Desmos Guide
Enter two points from the line of best fit
From the graph, pick two clear points the line passes through, such as and , and define them as points: A=(0,35) and B=(40,75).
Create the line through the points
Type y-35=((75-35)/(40-0))(x-0) to graph the line.
Read the value at x = 30
Type x=30 and look at the intersection of the vertical line with the best-fit line. Read the y-coordinate from the graph to get the predicted number of measures.
Step-by-step Explanation
Locate the given x-value on the line of best fit
Find on the x-axis (minutes practiced), then move up to the line of best fit.
Read the predicted y-value
From the point where you hit the line, move horizontally to the y-axis. The value is about measures, so the prediction is .