[Mithaldu]

The point here is: The website asked me about my beliefs. It did NOT ask me to work out the correct solution. And if i believe i cannot possibly give a useful estimate then that should be a viable answer i can give.

Your example is especially relevant since i don't even know what a gallon is. I guess it's maybe a liter or something? Who knows. Either way: Without actual research there is no more accurate modelling of my belief than "i don't know", period.