Believe it or not, some candidates tend not to ask further questions and launch straight into a very long, complex solution. What would you do if your boss gave you too little information? Was it an increase in CPC or CPA? Have competitors begun a bidding war? Did you turn on broad/phrase/exact matching. Do you have negative keywords?

If the question seems a bit vague or brief, ask the interviewer more questions to clarify!

My favorite response was the cheeky candidate that said: "If all else fails, reduce the budget by $400K and hire 3 developers and a dedicated SEO guy."