Logical Puzzle – 8 Coins and a Weighing Scale

logical puzzle 8 coin

One of the most commonly asked logical puzzle in interview of tech giants is the 8 coin and a “2 pan weighing scale” problem. Suppose you are given 8 coins and a 2 pan weighing scale which can compare the weights of two items on different sides. You are also told that one of the coins among the given 8 coins is fake and slightly heavier than the other 7 equal weights coins. Then you are required two find two things :

  1. The minimum number of weighings required.
  2. A method to find the fake coin with minimum number of weighings.

Can you tell the answer? If yes, then also provide a proper method to find the fake coin. Try yourself before seeing the answer.

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Nikhil Kr
Nikhil Kr
5 months ago

2 attempts required. Method 1: place 3 coins in each pan, if 1 side is heavier that means that pan has the fake coin. Then out of those 3 coins, place 2 coins in each pan of the weighing scale. If one side is heavier than other then that side has the fake coin and if both coins are of equal weight that means, the third coin is the fake.

Nikhil Kr
Nikhil Kr
5 months ago
Reply to  Nikhil Kr

Case 2: after placing 3 coins in each pan, if both sides are of equal weight then one coin out of the remaining 2 coins is the fake coin. Now place those 2 coins in each pan of the weighing scale, the heavier side has the fake coin.

5 months ago

Such a creative question

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