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Billiard Ball Problem
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Join Date: Oct 2007
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You have 9 billiard balls. They are all the same weight, save one. You want to find out which one is heavier. All you have is a scale that determines the heavier side. You can weigh any number of balls at any time. What is the least amount of weighings you can do to find the heaviest ball?
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Originally Posted by weasel7711 
You have 9 billiard balls. They are all the same weight, save one. You want to find out which one is heavier. All you have is a scale that determines the heavier side. You can weigh any number of balls at any time. What is the least amount of weighings you can do to find the heaviest ball?
Edit - I explained how, but after thinking about it, I took down the explanation in case other people want to puzzle over it themselves.
As a generalization, if you have n balls and one of them is heavy, how many weighings does it take?
Last edited by VernonDozier; Apr 1st, 2009 at 4:43 pm.
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correct me if im wrong (and might be the case) but if you got 9 billiard balls all of the same weight wouldnt the answer be 0 : none would be hevier as they weigh the same??
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Originally Posted by chriswellings
correct me if im wrong (and might be the case) but if you got 9 billiard balls all of the same weight wouldnt the answer be 0 : none would be hevier as they weigh the same??
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You have 9 billiard balls. They are all the same weight, save one. You want to find out which one is heavier.
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Join Date: Mar 2009
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lol... i read the q over and over mabee the question shoulda been worded a little different say they all weight the same excep one??
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Originally Posted by VernonDozier
Cool problem. You can do it in two weighings.
Edit - I explained how, but after thinking about it, I took down the explanation in case other people want to puzzle over it themselves.
As a generalization, if you have n balls and one of them is heavy, how many weighings does it take?
Never approach a computer with the words "I'll just do this quickly..."
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Originally Posted by Thinka
I've been thinking about it, and I can't work it out. Pray tell, what be the answer?
So after one weighing, you've narrowed it down to one of three balls. Randomly pick two of the three balls. Stick one ball on each side of the scale. Weigh them. If they weigh the same, the heavy ball is the ball that isn't on the scale. If one ball on the scale is heavier than the other, that's the heavy ball.
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