GMAT Focus scores as low as Q80 (
64%) with one wrong are just plain absurd.
One one hand, this does not surprise me: the GMAT's
adaptive scoring algorithm has always been very sensitive to mistakes—especially on Quant, and especially on easy/medium questions.
However,
under no circumstances should answering just one question incorrectly cost you a whopping 10 points, especially considering that the entire 21-question Quant section (scored from 60-90) contains only 30 earnable points.
Would this student have scored a perfect 90/90 if they had review-and-edited #7 to the correct answer? Evidence from other ESRs suggests that the answer to this question—whether fair or not—is
yes.