Use the math answer to get a good chuckle to show you have a good sense of humor, and then say "but, in all seriousness, etc etc etc." I agree with the advice to always put a positive spin on it, but it has to be honest and not something stereotypically interviewish. I always said that I was overbearing, and proceeded to talk about how I was probably too attentive in a previous job to the point of annoyance, the idea being that there is no thing as a lawyer that is too attenive.