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How can you find out which islander is the one that has a different weight?

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There is an island with 12 islanders. All of the islanders individually weigh exactly the same amount, except for one, who either weighs more or less than the other 11.

You must use a see-saw to figure out whose weight is different, and you may only use the see-saw 3 times. There are no scales or other weighing device on the island.

How can you find out which islander is the one that has a different weight?

posted Jul 9 by Kuldeep Apte

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1 Answer

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You start with 6 vs 6.
You take the side that is heavier and divide it 3 vs 3.
.
Option A, one of the sides is heavier.
This means the villager is heavier than the others.
You take the heavy side and divide 1 vs 1.
If a side is heavier than that villager is heavier. If the see-saw is in balance then the 3rd villager is the heavier.
.
Option B, the see-saw is in balance.
This means the villager is lighter and part of the other 6.
You divide the 6 from the lighter side and divide them 3 vs 3.
You take the lighter side and divide 1 vs 1.
If a side is lighter than that villager is lighter. If the see-saw is in balance then the 3rd villager is the lighter one.

answer Jul 9 by Jcm



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There are 12 people and a seesaw on an island, and you have the following information:

  • There is one islander who weighs differently than the other 11, but you don't know which one, nor if they are heavier or lighter.
  • You may use the seesaw to compare the weights of any two sets of islanders of your choosing.
  • Each of the twelve islanders is uniquely identifiable and can be weighed more than once.

What is the least number of times you need to use the seesaw in order to guarantee that you can identify the person who has the different weight?

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