Logic Puzzles · Billy-B
Logic Puzzle #48
From Billy-B's legendary 1001 Puzzle Collection — preserved on Puzz.com since 1998.
Puzzle #48
You have 8 marbles that weigh 1 ounce each, & 1 marble that weighs 1.5 ounces. You are unable to determine which is the heavier marble by looking at them. You have a weighing scale that consists of 2 pans, but the scale is only good for 2 total weighings. How can you determine which marble is the heaviest 1 using the scale, & in 2 weighings?
Reveal Answer
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.
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