Actually this is not really a maths question, more a logic one. Hope that's okay, I thought it might degenerate too much in chit chat.
This is one of a few questions posed in job interview. It's supposed to be answered quite quickly, it's simplicity reflects this. I'm just posting it here because, well, I like it and you lot might too.


You are given a bag of 24 marbles all identical is size and weight except for one which is ever so slightly heavier.

At you disposal is a set of scales.

How many times do you need to use the scales in order to determine which is the heavier marble?