Interview Brain Teasers Medium 2 min

You have eight identical-looking balls, but one is heavier than the others. Using a balance scale, what is the minimum number of weighings needed to identify the heavier ball?

Hint

Divide the balls into groups as evenly as possible.

Answer

2 weighings.

Explanation

Divide the balls into groups of 3, 3 and 2. Weigh the two groups of 3. If they balance, the heavier ball is among the remaining two and one additional weighing identifies it. If they do not balance, the heavier ball is in the heavier group of 3 and one additional weighing identifies it.

Step-by-Step Solution

Weigh 3 vs 3.
If balanced, weigh the two remaining balls.
If unbalanced, take the heavier group of 3 and weigh 1 vs 1.
Therefore 2 weighings are sufficient.

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