Re: Interview Question (with Shannon twist)

In article <5o6koi$r1s_at_mgh_cs1.mgh.com>,

        r#as#crystal_at_d#as#ri.mc#as#graw-hill.com (Rona Crystal) writes:
>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.

I have an extension to this question.
If the guy answered correct to the first question, you can ask him quick:

"What is the amount of information extracted from this experiment in Shannon(*) sense ?"

If he doesn't choke and tries to mention some logarithms of probabilities then take him; the guy is not only smart, but he also has a very strong math background. If the guy chokes and remains choked, still take him. He is still in the first 10% of population.

But I don't understand why do you need intelligence for a DBA ? ;-)

(*) Claude Shannon - The guy who invented a big chunk of information theory. Received on Fri Jul 18 1997 - 00:00:00 CDT