What a Good CFA Answer Explanation Actually Looks Like
An answer key is not an explanation. A good CFA explanation shows the worked steps that reach the answer, names the concept being tested, and explains why each wrong choice was tempting. Only that last part turns a missed question into something you learn from. If your practice bank just tells you "the correct answer is B," you are grading yourself, not studying.
I am the founder of FreeFellow and a CFA charterholder. When I was a candidate, the difference between a question bank I trusted and one I abandoned came down to this: did a wrong answer teach me anything, or did it just mark me down?
Why "The Answer Is B" Is Not Enough
When you miss a question, one of two things happened. Either you did not know the concept, or you knew it and fell for a trap. An answer key cannot tell the two apart. It cannot tell you whether you picked C because you flipped a sign, misread the question, or genuinely do not understand the method.
That distinction is the entire lesson. If you flipped a sign, you need a two-second habit fix. If you do not understand the method, you need to go back to the curriculum. A bare answer key sends both candidates away with the same non-information, and both are likely to miss the next version of the same question.
The Anatomy of a Good Explanation
A complete explanation has three parts.
- The worked steps. Not just the final number, the path to it. Which formula, which inputs, in which order. You should be able to reproduce it cold on the next question.
- The concept being tested. One or two sentences naming the idea the question is really about, so you can connect it to the rest of the curriculum instead of memorizing this one item.
- Why each distractor is wrong. This is the part most banks skip. Every wrong choice on a well-built question is engineered around a specific misconception. Naming that misconception is what inoculates you against it.
A Worked Example
Here is a Level I style question with the kind of explanation that actually teaches.
Question: A portfolio returns +50% in year 1 and -50% in year 2. What is its geometric mean (compound) annual return?
- A. 0.00%
- B. -13.40%
- C. -25.00%
- D. -12.50%
Correct answer: B.
An answer key stops there. A good explanation keeps going, choice by choice.
| Choice | Value | Why it is tempting, and why it is right or wrong |
|---|---|---|
| A | 0.00% | This is the arithmetic mean of +50% and -50%. It is the built-in trap: the arithmetic mean overstates compound performance whenever returns vary. It answers "the average of the annual returns," not "what you actually earned per year." |
| B | -13.40% | Correct. The geometric mean is the square root of (1.50 times 0.50), minus 1, which is -13.40%. This is the constant annual rate that reproduces the real two-year result. |
| C | -25.00% | This is the total return over the two years (0.75 minus 1), not the annualized rate. The question asks for the annual geometric mean, so this is one step short. |
| D | -12.50% | This is the total two-year return of -25% divided by 2, a simple average that ignores compounding entirely. |
The geometric mean is the actual compound rate of return. It equals the arithmetic mean only when every period's return is identical. Whenever returns vary, the arithmetic mean is higher, which is exactly why choice A is the trap and why "a portfolio that gains 50% then loses 50% is back to even" is wrong.
Notice what the per-choice notes did. If you picked A, you now know your error was using the arithmetic mean, a specific and common misconception, not a general weakness in "portfolio math." That is a targeted fix. The answer key alone would have left you guessing.
What to Demand From Any Explanation
Use this as a quick test of any CFA question bank, free or paid:
- Does it show the full worked solution, or just the final number?
- Does it name the concept, or assume you already see it?
- Does it explain the wrong choices, or only the right one?
- After a miss, do you understand the misconception you held, or only the letter you should have picked?
If the answer to the last question is "only the letter," the bank is testing you, not teaching you.
The Bottom Line
Practice questions are only as valuable as the explanations attached to them. Coverage and volume get the attention, but the explanation is where the learning happens. Demand worked steps, the concept, and a reason for every wrong choice.
FreeFellow is a CFA Institute Prep Provider, independent of CFA Institute, and does not promise a passing score. Every FreeFellow CFA Level I question carries a step-by-step solution and per-choice notes, free. See for yourself on the free CFA Level I practice page.