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A company has 10 machines that produce gold coins. One of

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Director
Joined: 26 Feb 2006
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A company has 10 machines that produce gold coins. One of [#permalink]  03 Jan 2007, 00:05
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A company has 10 machines that produce gold coins. One of the machines is producing coins that are a gram light. How do you tell which machine is making the defective coins with only one weighing?

http://www.gmatclub.com/phpbb/viewtopic ... ht=#282350
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Intern
Joined: 24 Feb 2006
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Mark the Machines 1,2, ......9,10 and assume each coin's weight Y gram

Take 1 coin from machine 1, 2 coins from machine 2, 3 from machine 3
......10 coins from machine 10; and weigh those together and u get X gram.
If there were no defective coins
total weight would have been = (1+2+3+4+........+10 )*Y= 55Y gram.

(55Y - X ) will give you the machine number of the defective one..
If (55Y - X ) = 2 Machine2 is defective
if (55Y - X ) = 10 Machine10 is defective
BTW.. this is not a GMAT type prob ...
Manager
Joined: 28 Aug 2006
Posts: 245
Location: Albuquerque, NM
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YEAH this is like a puzzle that some interviwer from deloitte may ask
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