Make a market on the number of UN member states
Interviewer: "Make me a market on the number of member states in the United Nations. I will trade either side, one contract settling at the true number."
Give a bid and ask, and explain what sets your width here versus quoting on a random coin or dice outcome.
Show a hint
This is a fact, fixed and knowable. The danger is not variance of a future draw; it is that your counterparty might know the number and you do not.
Your answer
This one is open-ended. Work it through, then check your reasoning against the full solution.