Here's a list of the deletions and their reason (note, I did not delete all of these so most is just guessing, but it's quite obvious why):
Four answers calculated the reaction for octane, not gasoline. They did not bother to check if that was a valid approximation. They often further calculated the reaction for ethanol, which is not part of the question. Actual answers for a gallon of octane (which is not gasoline): 8.25kg, 8.83kg, more than 8.3kg, 8.4kg
One showed a graph of the result (which incorrectly mixed up air and oxygen) without showing calculations or references. Actual answer: 5.9kg
One made an unreferenced point about not being able to equate gasoline and octane, then made a calculation using a model based on energy density. Actual answer: 9.287kg
One used a model based on atomic mass. Actual answer: 3 times the mass of fuel, which is not given nor calculated
One used an "average carbon atoms per hydrogen" calculation. Actual answer: 8.7kg
All of these answers got quite different results, some of them close to the value in the question, some not, some ...we don't know. No answer states how much uncertainty they have, so we can't really match their values to the question.
This shows that the answers are either displaying the error of false precision or they are altogether wrong. In any case: they are theoretical and this is why they were removed.
A side note on uncertainty, matching values and theoretical answers.
In science all, all measurable numbers are imprecise. Thus, it is essential to keep track of the uncertainty of values when performing any calculation. This is a quite interesting university level exercise, but it is certainly always done when "serious" science is made.
In scientific notation one either gives a specific uncertainty value, like so
meaning: 68% of the times this value is found to be within 8.6kg and 9.0kg
or if omitted, then the last given digit is assumed to have ±1 uncertainty
8.4kg → 8.4±0.1kg
meaning: 68% of the times this value is found to be within 8.3kg and 8.5kg
Therefore we can desume that the article in the question has found a value of 8.89±0.01kg, 3 significant digits.
As a first approximation it is possible to compare two uncertain value by checking whether their ranges overlap (in reality it's a bit more complicated since these ranges are probabilistic and we need to apply statistics).
If we want to compare any of the theoretical values found by our answerers with the claim, we need to know their imprecision (which we don't, because they did not calculate it).
This is fundamental and here's why. Do any of the calculated values confirm or disprove the claim? It depends on how many digits of the calculated values are significant:
- If we assume 1 digit of precision: 5 answers match the claim, 1 does not
- With 2 digits of precision: 2 answers match the claim, 4 do not
- Taking 3 or more digits of precision: no answers match the claim
Which is the correct interpretation? I don't know.
Unless a careful calculation and a careful comparison is made, it's really tricky to prove or disprove a claim with a theoretical answer, no matter how trivial the formula we use.