Challenge 101

The damn tomatoes

Difficulty level:

You have a 2-plate scale and 12 tomatoes:
- 11 has the same weight
- 1 has different weight (we don't know if it's lighter or heavier)

With only three weighings, find out which tomato is different and whether it is lighter or heavier.

* challenge sent by user Fábio Gomes Cordeiro.