Without getting into too many specifics (on rare occasions I pull it out again) it was a question of statistics and law of large numbers intuition. I was check

Without getting into too many specifics (on rare occasions I pull it out again) it was a question of statistics and law of large numbers intuition. I was checking for how directionally correct people would be on the subject, with 3 parts of the question to see how deep they knew it. More about intuition than actual computation. There was a subtle error on how aggressively to apply the law of large #s. How many times had I asked it? 50? I had a couple folks answer it like I thought it should be answered. He was the only who nailed it enough to catch the error too. The reality is interview performance is very different than work performance. Interview questions test interviewing ability more than anything else. Over time I've realized that the only reliable predictor of success is seeing people's work results first hand when they don't think they are interviewing. The danger is this too breeds issues of familiarity and lack of diversity, because one only hires from their narrow circle of the world. This makes it very tough to make college hires. The only things I've seen that worked are "High enough" GPA (with "High enough" being higher on non-technical majors) and some sign that the student had to significantly multi-task (lots of extra curriculars, research, or working through school). Most 21 year olds don't have interview training, so it's a very bad way to pick them.