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find the heavier ball

rehans oberoi
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Joined: Dec 06, 2005
Posts: 174
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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Joined: Sep 28, 2004
Posts: 1228
three


Thanks & regards, Srini
MCP, SCJP-1.4, NCFM (Financial Markets), Oracle 9i - SQL ( 1Z0-007 ), ITIL Certified
Srinivasa Raghavan
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Joined: Sep 28, 2004
Posts: 1228
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
lowercase baba
Bartender

Joined: Oct 02, 2003
Posts: 11175
    
  16

once. if i was lucky.


There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors
Stan James
(instanceof Sidekick)
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Joined: Jan 29, 2003
Posts: 8791
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.


A good question is never answered. It is not a bolt to be tightened into place but a seed to be planted and to bear more seed toward the hope of greening the landscape of the idea. John Ciardi
Bert Bates
author
Sheriff

Joined: Oct 14, 2002
Posts: 8806
    
    5
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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