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9 coins prob (Posted on 2016-01-18) Difficulty: 3 of 5
There are nine silver coins marked 1, 2, 3, 4, 5, 6, 7, 8, and 9.
They are supposed to weigh the number of grams that is written on them.
One of the coins is fake and is lighter than it should be.

Find the fake coin using the balance scale twice.

No Solution Yet Submitted by Ady TZIDON    
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Solution Outline of a sample solution | Comment 2 of 6 |
Weigh 169 v 358.

If they balance, the bad coin is in 247.
If left side is light the bad coin is in 169.
If right side is light the bad coin is in 358.

If 247 is bad, weigh 34 v 7. 
Balanced = 2 is bad.
Left light = 4 bad.
Right light = 7 bad.

If 169 is bad, weigh 36 v 9.
Balanced = 1 is bad.
Left light = 6 bad.
Right light = 9 bad.

If 358 is bad, weigh 125 v 8.
Balanced = 3 bad.
Left light = 5 bad.
Right light = 8 bad.

  Posted by Charlie on 2016-01-18 15:50:43
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