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find the heavier ball

 
rehans oberoi
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Suppose you had 8 billiard balls, and one of them was slightly heavier, but the only way to tell was by putting it on a scale against another. What's the fewest number of times you'd have to use the scale to find the heavier ball?
 
Srinivasa Raghavan
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three
 
Srinivasa Raghavan
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Put 4 balls each in Pan A & Pan B find the pan having the heaviest ball. Let it be pan b. So all 4 balls in Pan A are good balls, keep it seperate.
Now group the balls in pan b into two sets 2 in each pan. Find the Pan having the heaviest ball Let it be Pan A. Now you have identified 6 good balls.

Take one ball from Pan A and weigh it against any one of the 6 good balls if both are equal then the other ball is the culprit else this one should be the culprit.
 
fred rosenberger
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once. if i was lucky.
 
Stan James
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Two.














Put three on each side of the scale. If they match weigh the other two. If they don't match, weigh two of the heavy three.
 
Bert Bates
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for extra credit, show how if you had 12 balls, and one was either lighter or heavier, you can find the odd ball with only three shots at the balance.
 
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