The two formulae should be enough to answer any 3 set question, yes; the other formulae in the link you shared are just variations of it.
I suppose you could memorize a different variation for every possible question (i.e. isolate a different variable), but I really wouldn't advise it - it's unlikely you'll see more than 1 overlapping set question on test day and there are far more important topics on which to spend your time and brainpower.
I suppose you could memorize a different variation for every possible question (i.e. isolate a different variable), but I really wouldn't advise it - it's unlikely you'll see more than 1 overlapping set question on test day and there are far more important topics on which to spend your time and brainpower.

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto
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