Maths Olympiad Prep

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Problem 792

AMC 12 late, AIME early
Combinatorics Difficulty 4.4 Find the answer Harvard-MIT Mathematics Tournament · United States

Write down an integer from 00 to 2020 inclusive. This problem will be scored as follows: if NN is the second-largest number from among the responses submitted, then each team that submits NN gets NN points, and everyone else gets zero. (If every team picks the same number then nobody gets any points.)

The source for this one didn't record the answer, so there is nothing to check what you type against. Work it on paper and mark yourself against the solution below.

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Official solution

Solution:
The only Nash equilibria of this game (where each team plays its best possible move given the other teams' choices) are fairly degenerate: every team but one plays 11, and the remaining team is more likely to choose 22 than any higher number. Of course, we cannot assume perfectly rational play in reality - nor are the utility functions the same, since the goal is to score higher than other teams, not to maximize one's own expected number of points. It will be interesting to see what the submissions are.

Source: MathNet, licensed CC-BY-4.0. Statement reproduced verbatim; metadata (topic, difficulty, ordering) added by this project.