There are 16 coins, 3 of which are slightly heavier or lighter than the others. The counterfeit coins have the same weight but it is not known whether they are heavier or lighter than the genuine ones.
Using a balance scale, what is the minimum number of weighings in order to determine whether the counterfeit coins are heavier or lighter?
-All the coins look identical.
-The genuine coins have the same weight.
-You can compare any number of coins on the balance scale.
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