As is often the case, Randall Munroe has already delivered: https://xkcd.com/1602/. Perhaps the joke in this context would be if it said "bi-weekly".
"You should come to our Linguistics Club's bi-weekly meeting. Membership is open to anyone who can figure out how often we meet." (I mean, you have a 50-50 shot. I wonder if there's any personality insights one could learn from such a selection.)
"You should come to our Linguistics Club's bi-weekly meeting. Membership is open to anyone who can figure out how often we meet." (I mean, you have a 50-50 shot. I wonder if there's any personality insights one could learn from such a selection.)