Marketing positions cover a variety of roles, ranging from technical market analysis to creative storytelling. If interviewing for an analytical role, expect to answer statistical questions about market trends and patterns. If interviewing for a non-technical role, focus on highlighting your strong written and oral communication skills as well as your experience running compelling campaigns.
How many computers are there in Manhattan?
They just want to see your critical thinking and reasoning skills on display. Talk through your assumptions, and demonstrate that you have a basic working knowledge of the world (i.e. ~2 million residents, how many people commute in for work, what % of people own a computer, etc).