“Counting is hard. This is what I keep saying.”
It all stemmed from an arithmetic series problem with a known sum, but an unknown number of terms. As these things are prone to do, it let to a quadratic equation; as those things are prone to do, that led to two possible values for $n$, one of which was negative.
This is fine; there is no problem here; you discard the negative root as impossible due to the context, collect three marks and move on to the next question. Unless, of course, you’re @realityminus3, in which case you ask “what does the negative root…
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