[Stuey]

3 groups of 4 rocks is right
if they don't weigh the same or in the case of the type of scale I am using "balance" I remove 2 rocks from each side at the same time.

If that causes the scale to balance then I know I got the bad one in one of my mitts.

If the scale stays put then I can use the 4 stones I pulled as standard weighing ones to eliminate the remaining 4 on the scale with the previous method.

Basically I am cheating and using the scale more than 3 times but it does not apear that way as I am just removing the rocks in a certian order to help my deductions.

Makes sence to me but I describe it badly.