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  1. Brain Teasers
  2. You have 12 identical-looking balls and a balance …
Brain Teaser🔴 hardLogic

You have 12 identical-looking balls and a balance scale. One ball is a different weight (heavier or lighter). You have only three weighings to determine which ball is different and whether it is heavier or lighter.

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Divide into groups of 4. Weigh group 1 vs group 2. Based on the result, you can isolate the odd ball and determine if it's heavier or lighter in 2 more weighings using a specific decision tree.

Why this works

At first glance, this riddle may seem insurmountable, as it beckons you to identify a single odd ball among twelve, all while navigating the constraints of just three weighings. However, the clever trick lies in the strategic division of the balls into manageable groups. By weighing four balls against another four, you immediately glean vital information: if the scales tip, you've narrowed your search to one of those eight balls, and if they balance, you know the odd ball resides among the remaining four. The brilliance unfolds as you continue to subdivide your options based on the outcomes of each weighing. With each decision, you're not just isolating a suspect but also determining its weight relative to the others, whether it’s heavier or lighter. This decision tree method turns the riddle into a thrilling game of deduction, where each choice leads you closer to revelation, showcasing the power of logical reasoning and systematic elimination. This riddle reflects an age-old fascination with puzzles and problem-solving that dates back to ancient civilizations, where similar balance scale puzzles were used to test wit and intelligence. The "aha moment" comes when you realize that the methodical approach can yield clarity from chaos, a satisfying resolution that resonates with our innate love for solving mysteries. Fun fact: such balance puzzles are often featured in mathematical competitions and are a favorite among those who enjoy logic games, proving that sometimes the most mind-bending challenges can be tackled with a little creativity and strategy!

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Common Wrong Answers

“Weigh all 12 balls against each other in pairs.”

This approach would require more than three weighings, as you would need to weigh multiple pairs to determine the odd ball, making it impossible to identify the different ball within the given constraints.

“Weigh 6 balls against 6 balls.”

While this is a good initial step, it doesn't break down the problem effectively for the next steps. You can't isolate which of the 6 balls is different in only two more weighings after this, as it leaves too many possibilities.

“Use a single weighing to determine the heaviest ball and assume it's the odd one.”

This method ignores the possibility that the odd ball could be lighter. Additionally, a single weighing won't provide enough information to conclusively identify the odd ball or its weight difference.

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