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Your road trip is not going so well, a traffic jam delayed your schedule and you had to stop in a city you don't know to find a hotel. In a quick search on the internet, you found 3 hotels and decided that you will give them a shot. You may visit any number of hotels but once you leave a hotel you will not go back to back to it, you are just too tired for the trip back and forth. If you proceed optimally, what is the chance that you choose the best hotel to stay in?

1 2/3 1/2 1/3

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1 solution

João Areias
Dec 27, 2018

Let's number the hotels according to their quality being 1 the best hotel and 3 the worst. Let's choose a hotel at random to be the first one we visit and use it as a baseline, then we pick the first hotel which is better than the first one, this will work if we visit in the orders:

(2, 1, 3), (2, 3, 1) and (3, 1, 2)

and will fail if we visit the hotels on the orders:

(1, 2, 3), (1, 3, 2) and (3, 2, 1)

this gives you a chance of 1/2 of choosing the right one which is better than the 1/3 chance if you choose at random and it turns out it is the optimal solution in this particular case of the optimal stopping problem

I think you have to swap (3,1,2) and (1,3,2).

If I understood your strategy correctly, then for (3,1,2) you would leave 3 and search for a better hotel, but since there is none you would end up at 2. For (1,3,2) you would go to 1 and then find 3 as the next one that is better, so you would stay there.

Henry U - 2 years, 5 months ago

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I think you got the numbers swapped but the right idea, I said that 1 is the best and 3 is the worst, so for (3, 1, 2) I would go to 3 which would be my baseline, then I would go to 1 which is better and stay there. For (1, 3, 2) I have 1 as my baseline but since none are better than my baseline I end up at 2

João Areias - 2 years, 5 months ago

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Oh, now I see, I'm sorry.

Henry U - 2 years, 5 months ago

We have to go to the best hotel at last because only we will be able to find the best hotel. And the chance to go to the best hotel is 1/3.

Alapan Das - 2 years, 2 months ago

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If you know how the first hotel was and decide that you were going to stay in the first hotel that is better than the first, you will stay on the best hotel every time you visit the second best first, and when you visit the third best and then visit the best hotel immediately after.

João Areias - 2 years, 2 months ago

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