Stage: 4 Challenge Level: 
| There are 12 identical looking coins, one of which is a fake. The counterfeit coin is of a different weight to the rest. Using only a simple balance, what is the minimum number of weighings needed to locate the fake coin and how is this done? |  |
Number theory. Number - generally. Maximise/minimise/optimise. Manipulating algebraic expressions/formulae. Inequality/inequalities. Mathematical reasoning & proof. Patterned numbers. Visualising. Dynamical systems. Generalising.
Published April 1998.
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