Re: Interesting Puzzle
<font color="white"> Divide the marbles into 3 groups of four and compare the weight of two of the groups. If they weigh the same then one of the 4 unweighed marbles is the "bad" one, this is trivial to solve.
Otherwise you have 8 marbles that could possibly be bad (4 that could be light and 4 that could be heavy) and 4 marbles that you know are good. Call the 4 on the light side 1-4 and the four and the heavy side 5-8. Now compare the weight of marbles 1, 2, and 5 with the weight of marbles 3, 4, and 6.
If the scale now balances, either 7 or 8 is heavy, use the last weighing to determine which.
If side 1,2,5 is now heavy then either 3 or 4 is light or 5 is heavy. Measure 5 and 3 against two of the known good marbles. If side 5,3 is heavy, then 5 is heavy, if it's light then 3 is light and if it balances then 4 is light.
If side 3,4,6 was heavy in the second measurement then 1 or 2 is light or 6 is heavy. Weight 3 and 4 against two good marbles to find out which.
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