You have 9 weights, but you don't know how heavy they are. You also have a balance scale, which you can use to compare any two groups of weights. For example, you could compare the first two weights with the next three, and it would tell you whether the first group was less heavy, equally heavy, or more heavy than the second group.

In the least number of measurements, how can you find two equal groups of four weights if at least one such solution is guaranteed to exist?

  • $\begingroup$ It would take 2 measurements if only 1 was of a different weight but I assume the question does not assume that any 2 weights have the same weight. $\endgroup$ – Mohammad Zuhair Khan Dec 27 '17 at 9:50
  • $\begingroup$ Where does the question come from? Is it known to have a nice answer (not like 106 measurements and you need a computer to verify it’s minimal)? $\endgroup$ – Dap Dec 29 '17 at 9:10

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