A pile contains 11 indistinguishable coins. Precisely 9 of them are genuine each of which weigh exactly 10 grams.
However, precisely 2 of the coins are counterfeit. Each of these fake coins weigh either 9 grams and/or 11 grams.
Accordingly, both counterfeit coins may each weigh 9 grams; or, both of them may each weigh 11 grams; or, one of them weigh 9 grams, while the other weigh 11 grams.

Using only a traditional scale balance a minimum number of times, determine the counterfeit coins.

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