The scatterplot above displays the mean daily temperature and the number of ice-cream cones sold at a beach stand for eight randomly selected days. A line of best fit for the data is also shown.
According to the line of best fit, which choice is closest to the predicted number of ice-cream cones the stand would sell on a day when the mean temperature is ?
For scatterplot questions with a line of best fit, always work from the given model (the line) rather than from individual dots. Quickly locate the given -value on the horizontal axis, move up or down to the line, then move sideways to the vertical axis to read an approximate -value. Don’t worry about being exact—just estimate carefully and then choose the closest answer choice, keeping an eye out for choices that reflect common over- or under-estimates of your visual reading.
Hints
Use the line, not the dots
The question specifically mentions the line of best fit. Focus on that straight line rather than any individual data point when making your prediction.
Start from the temperature value
Find 23 on the horizontal axis (mean temperature). From that point, move straight up until you reach the line of best fit.
Then read across to the cones axis
Once you hit the line of best fit at , move horizontally to the axis labeled with the number of cones sold and estimate that value. Then pick the answer choice that is closest to your estimate.
Desmos Guide
Define a function for the line
For a verification, estimate two points on the line of best fit, such as and . Use them to enter the function in Desmos.
Evaluate the prediction
Enter in Desmos to find the predicted number of cones at . Compare the result with the answer choices and select the closest value.
Step-by-step Explanation
Use the line of best fit
The question asks for a prediction from the line of best fit, not from one of the individual data points. Find the point on the line whose horizontal coordinate is .
Estimate the vertical coordinate
Because is between the labeled x-axis values and , locate it between those marks and move vertically to the line of best fit. Then move horizontally to the y-axis.
The line is just below cones at this temperature, at about cones.
Choose the closest value
Compare the estimate of about cones with the choices. The closest choice is 200.