IBM Interview Question: I have a scale and 7 balls. 1... | Glassdoor

Interview Question

Intern Interview

I have a scale and 7 balls. 1 ball is heavier than all the

  rest. How do I determine the heaviest ball with only 3 possible weighing attempts?

Interview Answer

1 Answer


It only takes two attempts. Weigh six balls - three on each side of the balance. If they balance, then the 7th ball is the heaviest. If they don't balance, take two balls from the heavy side. If they balance, then the heavier ball is the one you didn't weigh. If they don't, then the heavier ball will be the one that tips the scale.

Michael Kraft on Mar 21, 2015

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