Reach 200

Logic Level 3

Dan and Sam play a game. Dan starts and says the integer 1 1 , then Sam says 2 2 . For each subsequent turn, the one who's next must say an integer that is strictly between the integer previously said and its double.

For example, Dan begins saying 1 1 , then Sam says 2 2 , and then Dan can say whichever integer he wants between 2 2 and 4 4 ; as the only integer between 2 2 and 4 4 is 3 3 , he must say 3 3 . Then, Sam can choose any integer between 3 3 and 6 6 ; that is, he can say either 4 4 or 5 5 .

The person who first says 200 200 is the winner. For the person who has a winning strategy, what is the minimum number of integers that he says?

Submit 0 0 if you think that nobody has a winning strategy.

Assumptions: Both players want to win the game.


This is the fourth problem of the set Winning Strategies .


The answer is 8.

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1 solution

Brilliant said that a better solution than 8 was found. I therefore tried 7... Winning strategy to get to 200 is to first get to 100: if you reach exactly 100, the other will have to say between 101 and 199 inclusive. Therefore you can say 200 next. The logic applies for 50, 25, 12, 6. So Dan will say: 1, 3, 6, 12, 25, 50, 100, 200 which is 8 numbers.

Sorry about that. I didn't spot a slight error in the report. I have updated the answer to 8.

Calvin Lin Staff - 3 years, 6 months ago

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