Predict the result
A student completed twenty practice problems and scored thirty-one. What are the prediction and residual?
Use the source’s fitted line.

Set up the model
Substitute twenty into twelve point five plus zero point eight x.
Residual means observed minus predicted.

Work the example
The prediction is twenty-eight point five.
Subtract twenty-eight point five from thirty-one.
The residual is positive two point five points.
The student scored above the line’s prediction.

Check the result
Now use twenty-five practice problems and an observed score of thirty-five.
Take eight seconds to think before the answer appears.
[Eight-second silent pause to work; the answer remains hidden.]
The prediction is thirty-two point five.
The residual is again positive two point five points.

Interpret the result
Positive residuals indicate that the model underpredicted the observed response.
Use the original task and check that your result fits its meaning.