J.P. Morgan Interview Question: puzzle 9 balls, identical in ... | Glassdoor

Interview Question

Analyst Interview(Student Candidate) London, England (UK)

puzzle 9 balls, identical in appearance. 8 are of same

  weight. 1 is heavier. Identify this heavier ball by using a scale twice.

Interview Answer

5 Answers


put 9 balls in groups of 3.

Interview Candidate on Apr 3, 2011

Split them into two sets of 4 and 1 individual ball. Place the two sets on each side of the balance. If the sets balance out, then the individual ball is the heavier one. If the sets don't balance, then take the heavier set and split it up into two sets of two and repeat.

Anonymous on Apr 9, 2011

I believe that an explanation to the solution that Interview Candidate is suggesting can be found here:

sqr23 on Apr 15, 2011

Split the balls into groups of three, compare two of the groups. If the sets balance then the heavy ball is in the third group, otherwise it is in the group left out. Whichever it is, take two balls from that group to weigh. If they balance, you know it is the third ball, if they don't, you have the heavier ball.

Anonymous on May 31, 2011


an87 on Jun 13, 2011

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