太長唔想用中文打
The strategy of choosing 100 is a weakly dominant strategy.
Consider a player, Alice. We only need to consider two cases:
Case 1: The largest number chosen by the rest of the group is strictly less than 100. Then, Alice can always win by choosing 100, but if she may lose if she chooses a number less than 100.
Case 2: The largest number chosen by the rest of the group is 100. Then, Alice will lose no matter which number she chooses, so she is indifferent between all possible strategies.
The conclusion means that all (rational) players should choose 100, leading to a Nash equilibrium outcome in which all players gain zero point.
You are incorrect. You analysis only work when it's a 1vs1 game. A university entrance exam should have more than 2 people, so there is no Nash equilibrium.
Consider this counter example for your Case 2:
Two or more people chose 100, the rest chose 1-98. Now Alice can win by choosing 99. Therefore, your Case 2 is not true.