Hey there,
Two things. Well, three. Firstly - great score!
Optional Essay: No, don't write about this. There is no good reason you got a 58th percentile that would justify the use of an optional essay. Keep in mind, it's there to help explain things but if you do a poor job at it or have a less than adequate reason, it will do more damage than good. Not using your math skills for 6 years doesn't mean you couldn't have studied. I'm saying this from the perspective of an admin director who is reading the reason / excuse. If it is hard to differentiate between the two, then assume they'll think it's an excuse.
The ratios: There is no rule anywhere that states any school wants to see a certain percentile or above in any particular portion. Ok, do they want to see higher scores and balance? Of course. But the whole 80/80 rule (or in this case, 75/75) is something someone said at some time and it stuck. Does your 58th percentile score raise some questions? Absolutely. Verbal carried you and that's the truth. But there are many ways in an application to show you have the skill set to handle the academic rigors that come with an MBA program.
Also, you had an amazing trajectory between test #1 and #2 and that's a good story! Why try to write an optional essay that takes away from it with what most will assume is a weak attempt at an excuse (regardless of what it is)?
I hope that helps and congrats again on the 710!
Bhavik
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