2015 UNM-PNM Statewide High School Mathematics Contest II Problems/Problem 4

Problem

There are $12$ coins in a parking meter and we know that one of them is counterfeit. The counterfeit coin is either heavier or lighter than the others. How can we find the fake coin and also if it is heavier or lighter in three weighings using a balance scale? Hint: $4=3+1$.

Solution

See also

2015 UNM-PNM Contest II (ProblemsAnswer KeyResources)
Preceded by
Problem 3
Followed by
Problem 5
1 2 3 4 5 6 7 8 9 10
All UNM-PNM Problems and Solutions

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