Logical Puzzles Hard 3 min

You have 9 visually identical coins and exactly one is heavier. Using a balance scale, what is the minimum number of weighings required to guarantee finding the heavier coin?

Hint

Divide the coins into three equal groups.

Answer

2 weighings.

Explanation

Divide the coins into three groups of three. Weigh one group against another. If balanced, the heavy coin is in the third group. Otherwise it is in the heavier group. A second weighing of two coins from the selected group identifies the heavy coin.

Step-by-Step Solution

1. Divide into 3, 3 and 3.
2. Weigh group 1 against group 2.
3. Select the heavier group or the unweighed group if balanced.
4. Weigh two coins from that group.
5. If they balance, the third is heavier; otherwise the heavier side identifies the coin.

6 puzzles

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Medium

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Hard

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Hard

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