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Three Heavy and Three Light Balls Puzzle - Solution
The Puzzle:
Three out of six look-alike balls are heavy. The other three are light.
How many weighings on a beam balance are necessary to identify the heavy balls?
(A Martin Gardner puzzle)
Our Solution:
Three weighings suffice. There are two different techniques for solving the problem. Let the balls be numbered 1 thru 6.
1. Weigh (1,2) vs (4,5), then (2,3) vs (5,6), then (3,1) vs (6,4).
2. All weighings involve one ball on each side of the beam balance. First weigh 1 against 2. If these are equal, then weigh 1 against 3, otherwise weigh 3 against 4. The reader may work out what the third weighing should be.
Puzzle Author: Martin Gardner