I have hardly ever talked about the GMAT Algorithm. Rather, I ask my students not to worry about how algorithm works and to just focus on their preparation.

However, I came across a post on GMAT Club that highlighted an aspect of the GMAT Focus algorithm that I had not considered. The post was from a student who scored 81 percentile in the Quant section despite getting just one question wrong.

This was very surprising for me. If you get all questions right, you get Q90 (100 percentile) in the Quant section.  With just one question wrong, how can your score drop to Q83 (81 percentile)?!

After going through the discussion on the thread (credit to Marty Murray’s insightful comments), I realized that a person could see a significant drop in the score by getting just one or two questions wrong if the person:

1. initially got more questions wrong among the initial questions (the first 5-10 questions)
2. but later got them correct by using the option to edit answers (On GMAT Focus, you can edit up to 3 answers per section.)

This is what happened to the person who got Q83 with just one question wrong. He initially got more questions wrong—he initially got Q1 and Q4 wrong, too, but later changed their answers to the correct ones. 

However, since he initially got three questions (Q1, 4, and 5) wrong among the first five, he never saw hard or very hard questions in his exam. As a result, he got a low score despite getting only one question wrong.

Given the test’s adaptive nature, this behavior is logical. The test adapted to his initial sub-par performance and showed him easy and medium questions. Even though he later corrected two out of his three mistakes, he did not deserve to score the same as someone who correctly solved many hard and very hard questions on his test.

While this behavior is logical, I had not considered it. I expect many people to sit for the exam without being aware of such behavior. Some may want to randomly mark an answer to a question and move on, relying on the feature to edit their answer later.

However, you now need to be aware that if you do so in the initial few questions, you will bring down the difficulty level of your test. This may have a significantly negative impact on your score.

Thus, I have the following recommendation for the people taking the GMAT Focus exam:

1. Attempt the first half of each section as if the option to edit answers does not exist.
   1. This DOES NOT MEAN that you try to get all these questions correct, regardless of the time it takes.
   2. This means you give your best to solve the questions you can solve within the time limits.
   3. This also means that you can randomly mark an answer to the question you cannot solve, just as you would even if the option to edit answers did not exist. 
2. In the second half, you may take advantage of the option to edit answers by randomly marking answers to questions you find hard. You can return to these questions at the end if you have time.

Let me know if you have any questions.

Reference: https://bit.ly/3KbyP1M