[logfromblammo]

In the real world, a light source has a useful radius of illumination. This could be exploited. If the useful radius is greater than half the span of the bridge, everyone can cross the bridge in exactly 10 minutes.

If the useful radius of the torch is 25% the bridge length, the bridge can be crossed in 15 minutes.

So the correct answer to the puzzle question is "how much of the bridge does the torch illuminate?"

Then the questioner gets flustered, and you can suggest, "Maybe you should have given them one set of night-vision goggles instead."

If you solve the puzzle as written, you can only be as clever as the puzzle-maker. If you can break the puzzle and then fix it, you must be cleverer.

[interdrift]

I don't think that would make the person who's interviewing you very happy.

[logfromblammo]

I have interviewed enough times to know that you can't please everybody. And some interviewers like to assert their dominance during the interview. If they see you as a potential competitor rather than an underling, they won't endorse you.

I once aced an interview brainteaser, and the interviewer actually tried to derail my solution by interrupting and making misleading suggestions. When I finished, he told me that I was the only candidate so far to give the "correct" answer. He was clearly unhappy about it, which confused the heck out of me at the time.

I wasn't supposed to do that. I was supposed to give a half-assed, partially correct answer and let the other guy show off how smart and superior he was, by giving me the "real" answer.

So yes, beating the brainteaser might backfire. If it could, would you still want to work there?