Trying to recall a problem about balls.
There are 30 balls of 10 colors, 3 of each color. One of each 3 balls form the same color is fake. You are allowed to pass several balls, and see whether there are fake balls among them or not. Needs to find all 'fake' balls with 7 checks.
Please ignore all numbers, I don't remember. And probably those were't balls, maybe bombs)
Sorry if this isn't the right place to ask this question.