Hrm, if someone answers "I'd google it," I consider that to be a completely valid response. Of course it automatically invites the follow-up, what if a google search fails?
[1] At least to the extent that the public is concerned. It is possible that some skunkworks operation has solved it in secrecy.
Alternative: it's a completely contrived problem. Interviewers really don't like it when you point that out, though. :-)