# Tips for AP Statistics Free-Response Questions

There are many helpful strategies for maximizing your performance on free-response questions, but actually doing so is a learned skill. Students are often too brief or give incomplete responses. Don’t assume the reader will fill in the blanks for you. You have to know the material to do well on the free-response, but knowing the material alone is not sufficient—you must also demonstrate to the reader that you understand the statistics in the context of the question. Many of the following tips will help you do just that.

1. Read all parts of a question first before beginning. There’s been a trend in recent years to have more and more subparts to each question (a, b, c, …). The subparts are usually related, and later parts may rely on earlier parts. Students often make the mistake of answering, say, part (c) as part of their answer to part (a). Understanding the whole question first can help you answer each part correctly.

3. Answers alone (sometimes called “bald” answers) may receive some credit but usually not much. If the correct answer is “I’m 95% confident that the true proportion of voters who favor legalizing statistics is between 75% and 95%” and your answer is “(0.75, 0.95),” you simply won’t get full credit. Probability questions generally require that you show some calculation, even if it is a simple one. And be sure to include units when appropriate.

4. Answers must be in context and justified. A conclusion to an inference problem that says, “Reject the null hypothesis” is simply not enough. A conclusion in context would be something like, “Because the P-value of 0.012 α = 0.05, we reject the null hypothesis and conclude that there is convincing evidence that a majority of people favor legalizing statistics.”

5. Make sure you answer the question you are being asked. Brilliant answers to questions no one asked will receive no credit. (Seriously, this is very common—some students think they will get credit if they show that they know something, even if it’s not what the question asked.) Another too-common mistake is doing all the calculations needed to support an answer, but never giving the answer! Be sure to look back at the question, then at your response, to be sure you answered the question.

6. Procedures are to be identified by name or by formula. Copying the correct formula (correctly) will count as identifying your procedure. Correctly substituting the appropriate values into the formula can also save you if you make a calculation error. On the other hand, using an incorrect formula or incorrectly substituting numbers can cost you. Writing the name of the procedure and giving the answer is sufficient, but can not help you if you make a calculation error.

7. If you are using your calculator to do a problem, don’t round numbers until you have the final answer. Don’t round off at each step of the problem as that creates a cumulative rounding error and can affect the accuracy of your final answer. There is no hard rounding rule, but be reasonable. Don’t round means or expected values to whole numbers, but don’t keep 8 decimal places, either. A good guideline is to round means to two decimal places beyond the precision of the data, and standard deviations one place beyond that. Make sure that any reference to calculator commands has been accompanied by an appropriate explanation of their usage, and that all parameters are defined.

8. Try to answer all parts of every question—you can’t get any credit for a blank answer. On the other hand, you can’t snow the readers—your response must be reasonable and responsive to the question. Never provide two solutions to a question and expect the reader to pick the better one. In fact, readers have been instructed to pick the worse one. Cross out clearly anything you’ve written that you don’t want the reader to look at.

9. You don’t necessarily need to answer a question in paragraph form. A bulleted list or algebraic demonstration may work well if you are comfortable doing it that way.

10. Understand that Question #6, the investigative task, may contain questions about material you’ve never studied. The goal of such a question is to see how well you think statistically in an unfamiliar situation. The best way to prepare for this question is to practice investigative tasks. Work on applying what you know in a variety of new situations.