This goes the same way as the "quadruple gear" achievement and you will unlock it near the end of the game. Funny thing is, that after you'll unlock it, there will be more questions "for the little grey cells" coming, but they don't seem to count towards the achievement.
Nevertheless: If you should be struggling for one of those, you can always "use a clue" from the ingame menu (press
). This doesn't affect any achievements whatsoever and can always be used if you're struggling with the game.