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 Scale game (Posted on 2003-08-06)
This problem is a combination of a traditional weights and scales puzzle and a probability puzzle.

You are given the traditional scale balance and a set of 10 coins. You know that in this set of coins there are four fakes - two that are heavier than the others, and two that are lighter. Furthermore, you know that a light coin plus a heavy coin will perfectly balance two genuine coins. You are permitted only two weighings with the balance and asked to pick one of the 4 fake coins. What strategy should you use to maximize your success rate, and what would your success rate be?

What if you were given one genuine coin to start with (though still leaving you with 10 unknown coins)?

 See The Solution Submitted by Cory Taylor Rating: 4.2000 (5 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
 Better than 50% | Comment 7 of 10 |
I got a 5/6 = 83.33% success rate using a known genuine coin and a 29/35 = 82.86% success rate without a known genuine coin.
 Posted by Brian Smith on 2003-09-02 09:44:56

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