Microsoft Interview Question: You are given nine balls, one... | Glassdoor

Interview Question

Finance Intern Interview

You are given nine balls, one of which weighs less than the

  rest. You are also given a traditional two-sided scale. How many times do you need to weigh balls to determine which is the lightest one?

Interview Answer

1 Answer


2 weighings
Seperate balls into 3 groups of 3. Put a group of 3 on each 1/2 of the scale. If the scale balances, the the light ball is in the 3rd group. If they don't balance, then you know the ball is in the 'light' group.

Clear the scales and put one ball from the light group on each side of the scales. If the balance, then it's the 3rd ball.

JG on Jan 17, 2013

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