I picked this up at an AISD training years ago and have loved it ever since. It's pretty straight forward, but I really like this one. It makes kids stop and think. The ones who get an "answer" first are taught a quick lesson. I don't ever say, Oh you got it!! My response is an invitation to investigate further. Actually I usually just let them sit there thinking they got the one and only answer. When they overhear someone talking about their own answer...and it's different from theirs, they get back to work quickly!! Once they catch on that there is more than one answer, I encourage them to organize their data and look for a pattern.