Quote:
Originally posted by Bungleau:
There are 8 marbles that weigh 1 ounce each, and 1 marble that weighs 1.1 ounces. The marbles are all uniform in size, appearance, and shape. You have a balance that contains 2 trays. You are only able to use the scale 2 times. How do you determine which marble is the heaviest using only the scale and marbles in 2 weighings?
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Weigh marbles 1,2,3 vs. 4,5,6. If they're equal, than the heavier one is either 7 or 8. Weigh 7 vs 8 and take the heavier one.
If 1,2,3 vs 4,5,6 is not equal, take the heavier group. Say it's 1,2,3. Now weigh 1 vs 2 and take the heavier one. If they're equal, it's 3.
Try this one: You've got a 4 minute hourglass and a 7 minute hourglass. How do you measure exactly 9 minutes?