view puzzle related to this thread.
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divide the 9 marbles into groups of 3 i.e. each having 3 marbles.....now place the 2 groups of the marbles on the scale, if the scale is balanced then it means that the third group must be having the heavier marble, or one of thoso groups is having the heavier marble...

Once we have determined the group with heavier marble, then place any 2 marbles of that group on to the scale , in case the scale is balanced then the 3rd marble of that group must be the heavier one. or else scale points the heavier one of the 2 being weighted.....