Which number should replace the question mark in the series 2, 8, 26, 80, ?

Each term is three times the one before it plus two: $2\times 3+2=8,8\times 3+2=26,26\times 3+2=80$. So the next is $80\times 3+2=242$. Answering 240 comes of trebling and forgetting to add the two; 162 of doubling and adding two; 244 of adding four instead of two.