This isn't a brain teaser, they actually correlate with on-the-job performance. When I worked at Google I looked up their internal reports on the subject and they showed that the score people got on these algorithm interviews correlated pretty well with their performance ratings after they got hired. In other words the group of people who got hired even though they had low scores performed significantly worse than the people who got hired with excellent scores.
Edit: This applies for senior engineers as well.