Impossible Interviews

The issue of how the question is supposed to differentiate between candidates is tricky. Any questions (trick or straight) should give the interviewer some sort of insight into how well or badly the candidate will do the job. Had I been asked to add all the numbers from 1 to 10 in an interview I could have immediately responded with 55 as this is something I know (without having to go through the arithmetic series method, which I also know), but this does not affect how well I do my job either way. I could also point out that being pretty good at mental arithmetic, if I had to do the sum '1+2+3....' I could probably complete it faster than some could do the "(1+10)*10/2" calculation, so how could the interviewer know how I had arrived at the answer? James's sum of one to one million is a better differentiator, but why not make it 1 to 37 or some other random number? I therefore can't see that this question has any bearing on differentiating between candidates.

When interviewing my method is to ask questions to probe the candidates knowledge around the job to be done. Some of them may be 'impossible questions' on the basis that it is exceptionally unlikely that anyone will be coming into the job with 100% of the needed knowledge and they will therefore be unable to answer all of the questions, but the knowledge of the candidates limitations gained at the interview will identify how much training/on-the-job learning will be necessary before the candidate is fully functional. It also identifies candidates such as Andy who admit they don't know the answer but can show they know where to look to find out. This does not mean it is an impossible interview, as I only ever had one candidate who was able to provide all the answers, though given his background I would have been surprised if he couldn't. I went ahead and asked the same questions as the other candidates had been asked to make the process fair (and I had two vacancies so I still needed to consider the best of the other candidates).

Alasdair

The issue of how the question is supposed to differentiate between candidates is tricky. Any questions (trick or straight) should give the interviewer some sort of insight into how well or badly the candidate will do the job. Had I been asked to add all the numbers from 1 to 10 in an interview I could have immediately responded with 55 as this is something I know (without having to go through the arithmetic series method, which I also know), but this does not affect how well I do my job either way. I could also point out that being pretty good at mental arithmetic, if I had to do the sum '1+2+3....' I could probably complete it faster than some could do the "(1+10)*10/2" calculation, so how could the interviewer know how I had arrived at the answer? James's sum of one to one million is a better differentiator, but why not make it 1 to 37 or some other random number? I therefore can't see that this question has any bearing on differentiating between candidates.

When interviewing my method is to ask questions to probe the candidates knowledge around the job to be done. Some of them may be 'impossible questions' on the basis that it is exceptionally unlikely that anyone will be coming into the job with 100% of the needed knowledge and they will therefore be unable to answer all of the questions, but the knowledge of the candidates limitations gained at the interview will identify how much training/on-the-job learning will be necessary before the candidate is fully functional. It also identifies candidates such as Andy who admit they don't know the answer but can show they know where to look to find out. This does not mean it is an impossible interview, as I only ever had one candidate who was able to provide all the answers, though given his background I would have been surprised if he couldn't. I went ahead and asked the same questions as the other candidates had been asked to make the process fair (and I had two vacancies so I still needed to consider the best of the other candidates).

Alasdair