They don’t want to hear the answer “no.” In fact, it may not occur to them to ask a question that may yield a no.
So the author's obviously never heard of sanity checking, in fact that's the second thing that I always do once I confirm a solution is to confirm it's not a fallacy.
Having said that, my solutions were -10 -20 -40 -10 -8 -4 1024 1026 1030
and I said it was +2, +4 and got it wrong!