### 27 Coins Weight 10 Grams Except 1

You have 27 coins, each of them is 10 grams, except for 1.

The coin which is different is 9 grams or 11 grams (the coin is heavier or lighter by 1 gram).

You can use balance scales that compares what is in the two pans and compare two groups of coins to find the lighter coin.

What is the minimum number of weightings that can guarantee to find the different coin?