This answer is for 2 weighings. The problem I originally had
posted here was for 3 weighings, but since you can complete the problem with 2
weighings, I list only the most efficient method. Place 3 marbles on each pan.
If they balance, remove the marbles from the pans, & place 2 of the
remaining unweighed marbles on the pans, 1 on each pan. If 1 is heavier, it is
the heavier marble, but if they balance, the remaining unweighed marble is the
heavier 1. If your first weighing does not balance, remove the marbles from the
lighter pan, & place 1 marble on each pan from the heavier pan. The heavier
1 is the 1.5 ounce marble, but if they balance, then the marble from the heavy
pan from the first weighing that was not weighed in the second weighing is the
heavy 1. |