Question

You've got 27 coins, each of them is 10g, except for 1. the 1 different coin is 9g or 11g (heavier, or lighter by 1g). you should use balance scale that compares what's in the two pans. you can get the answer by just comparing groups of coins. what is the minimum number weighings that can always guarantee to determine the different coin. display answer

Answer 1

Separate the coins into 3 stacks of 9 (A, B, C). Weigh stack A against B and then A against C. Take the stack with the different weight (note lighter or heavier) and break it into 3 stacks of 3 (D, E, F). Weigh stack D against E. If D and E are equal, then F is the odd stack. If D and E are not equal, the lighter or heavier (based on the A, B, C comparison) is the odd stack. You now have three coins (G, H, I). Weigh G and H. If G equals H, then I is the odd and is lighter or heavier (based on the A, B, C comparison). If G and H are not equal, then the lighter or heavier (based on the A, B, C comparison) is the odd coin.  

Answer 2

Answer:

3

Step-by-step explanation:

1. Divide the 27 coins into three groups of nine coins each.
2. Weigh two of them separately. If they balance, the third pair of coins is faulty. Otherwise, the pan with the faulty coin will remain on top.
3. Divide the defective nine-piece set into three sets of triplets. To find the triplet containing the defective coin, repeat step 2 above.
4. Weigh two coins from the problematic triplet to repeat process 2 and identify the defective coin.

As a result, three weighings are sufficient to detect the faulty coin.

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