AP Stats FRQ Practice Prompt Answers & Feedback (Unit 2)

The FRQ Unit 2 Exam Practice Prompt

FRQ Writing Samples & Feedback

FRQ Practice Submission 1

Teacher feedback

In part (a), you do a good job of describing “negative,” but your descriptions of “strong” and “linear” fall a little bit short. For “strong,” it’s not clear what you mean by “same correlation.” If you’re referring to a similar rate of change, that would fit under “linear.” The word “strong” refers to the idea that the predicted values of # of therms used are typically close to the actual # of therms used; that is there are small residuals based on the regression line. For “linear,” I’m actually unsure if your description would get credit or not - you should be referring to how the points on the scatterplot appear to create a straight line.

In parts (b) and ( c ), you have strong explanations and would earn full credit for both parts. Overall, this is well done!

FRQ Practice Submission 2

Teacher feedback

In part (a), your responses are clear and concise. For the description of “negative,” you could strengthen your response by saying “tends to decrease,” but your response would earn credit as-is.

In part (b), I would be careful to include units in your response (“degree” should be sufficient but adding “Fahrenheit” can strengthen, and you should include “therms” for the natural gas). Your sentence works as written, and “expected” will work as a substitute for “predicted” or “on average,” which is what’s typically written on AP rubrics.

For part c, you’ve correctly interpreted the residual, but reversed the units. The residual was for the number of therms being used (so we used 6.42 therms less than predicted); assuming you show your math on the real exam (hard to do in this forum, I know), you would likely earn partial credit for that mix-up.

FRQ Practice Submission 3

Teacher feedback

Your answer to part (a) communicates everything it needs to, and includes context of the problem. In part (b), you’ve state everything clearly and including the expression “on average” at the end of the sentence makes it clear that this is a prediction, not a guarantee. You would earn “essentially correct” (E) for both parts a and b. For part ( c ), be careful: the 51.412 you’ve calculated is the number of therms, and is a predicted value (not an observed value). Therefore, the residual should be negative instead of positive (as we’d do 45 - 51.412). Given both the reversal of signs and the incorrect units in your interpretation, it is likely that you would be scored “incorrect” (I) for that part of the problem.

FRQ Practice Submission 4

Teacher feedback

In part (a), you make good use of context throughout your answers. Be careful that when you’re describing the scatterplot, you are making references to x and y (not y-hat), since the scatterplot contains actual values. You should also say things like “as the average daily high temperature increases…” in your description of “negative” and “linear” (your answers left of the “as”).

In part (b), your sentence framing is good, uses correct units, but misses a key thing that “gets” a lot of students on these types of problems: you’re missing “non-deterministic” language for the “decrease by 1.698 therms” part of your sentence. That’s the AP rubric’s fancy way of saying "you make it sound like it will decrease by this much, when it is only predicted to decrease by this much on average. You’ll need to use “predicted,” “on average,” “estimated,” or similar words when describing slope or intercept. Your answer would earn partial credit.

In part ( c ), you correctly calculate and clearly interpret the meaning of your answer in the context of this problem. Nicely done!

FRQ Practice Submission 5

Teacher feedback

In part (a), your answers are clearly-written and presented in context. All three descriptions are correct; you would earn full credit.

In part (b), you are missing one key word that would make your answer complete, and it would be enough to mark you down to partial credit: something like “predicted” or “expected” when talking about the change in response variable. We should say something like “…the average household usage of natural gas is predicted to decrease by 1.698 therms”. This is a common error, so watch out for it.

In part ( c ), you perform the residual calculation correctly and describe the meaning of it in context. Full points!

FRQ Practice Submission 6

Teacher feedback

In part (a), you clearly detail the meaning of the words “negative,” “linear,” and “strong,” including units and context along the way.

In part (b), you give a correct description of slope - including the key phrase predicted. You can strengthen your answer by including units on the response variable (therms, in this case).

In part ( c ) , you correctly calculate the residual. On the “real exam,” you’d want to show where the -6.412 came from. In your explanation of what it stands for, you should also use the number 6.412 in some way (by saying, for example, “which is 6.412 therms lower than the predicted value…”).

FRQ Practice Submission 7

Teacher feedback:

You answer is very thorough! All three parts address what is asked in the question (without anything unnecessary added), and you use appropriate language such as “predicted” in part b and provide answers in context and with appropriate units. You would likely earn full credit on all parts. Well done!