Re: Interview Question

In article <FscdMLASQZozEwmG_at_jbdr.demon.co.uk>, Jeremy_at_jbdr.demon.co.uk says...
>
>In article <33A06770.161E_at_aig.vialink.com>, Johnny Barnes
><jbarnes_at_aig.vialink.com> writes
>>Last summer I interviewed with a large airline firm for a dba position
>>and the first technical question asked was - If you have 8 marbles all
>>of the same size but one is heavier how can you find the heavy marble
>>with a set of balance scales in just 2 weighings?
>
>Well clearly you'd need 3, so I guess this must be a lateral thinking
>test - probably involving some highly debatable "trick".
>
>What was the answer and did you get it correct?
>
>--
>Jeremy Rickard

No trick here, just have to look beyond the obvious, but I'm not sure that I could have come up with the answer under pressure of an interview.

Divide the marbles into three groups of 3, 3, and 2. Put both groups of 3 on the scale (weighing #1). If they balance the heavy one is in the 2 group and you put each of those on the scale (weighing #2) and you have found it.  If the two groups (in weighing #1) of 3 do not balance, you know with group has the heavy one so weigh (alternate weighing #2) any two of them and you now know which one of them it is.

While skills like this may come in handy in identifying and solving problems, I'm not sure the lack of the correct answer is meaningful. The first time I read the question in the original post, I thought about it but couldn't get the answer. When I saw it repeated in this post, the answer just popped into my mind. So, so I guess that I would have missed it on the interview.

-- 
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