REI Systems Interview Question: I have 9 coins, out of which ... | Glassdoor

Interview Question

Software Engineer Interview Herndon, VA

I have 9 coins, out of which 8 coins are identical in

  weight and one is lighter in weight. Is it possible to find the light weight coin with only two weighings, using pan balance?

Interview Answer

2 Answers


Yes, in 2 weighings.

Interview Candidate on Mar 16, 2010

Yes. Put 3 on one side, 3 on other and set aside 3. If the pan tips, the lighter group rises up, if equal, the lighter group is on table. Once you find the lighter group of three, use the same tactic, one coin on table, one in each pan. If it tips, you found the lighter one, otherwise it is on table.

Same question is asked with balls and with groups of 8.

PuddinHead on Mar 17, 2010

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