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Which is Which (Posted on 2006-07-07) Difficulty: 3 of 5
You have six balls - three red and three black. All the red balls weigh differently, i.e. one of them is heavy, the other medium, and the third light. Each red ball has a black twin of the same weight. A heavy and a light ball put together weigh as much as two medium balls.

What is the least number of weighings required on a balancing scale to determine which is which?

No Solution Yet Submitted by Salil    
Rating: 3.0000 (2 votes)

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needs checking | Comment 7 of 15 |

I think you can do it in three weighings.

124 against 356

125 against 346

25   against 14

note: red balls are numbers 1,2 and 3

I also have poss second weighing 154 / 326 but third weighing would need modifying.

Depending on results one has to reason pairings and weights.

I'm checking it through but even if not right I believe there is a three weigh solution based on one of these two first and second weighings. The reasoning is a little difficult but possible.

Anyway it's a line of attack if anyone can modify it or prove/disprove it I'd be grateful

  Posted by ant simmons on 2006-07-09 19:44:26
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