When solving a problem, make sure to do so in a clear and logical way, explaining out loud why you're doing each step. Talk through your roadblocks and give examples of how you'd find the solution in the "real world". Often, that answer would be to Google for some particular function. Say so! They know you're not a Ruby expert, but they need to know that you'll be able to seek out solutions to the problems you'll inevitably encounter on the job.