There’s a spectrum of reasonableness with technical interview questions—the process described in this post is unreasonable, but I think plain old fizzbuzz is about as reasonable as it gets. It’s actually pretty “real world” if the candidate will be writing code in their job.
It’s not a trick question nor does it require memorization or study to prepare. You’re not being given 20 minutes to solve something that requires knowledge of an algorithm that researchers worked on for decades that you’ve either practiced or will stumble through deriving from first principles—you’re writing a very simplistic function.
The only thing that might be tricky about FizzBuzz is if the person doesn't know about the modulo operator. I can't remember the last time I used it in production code; I use it far more thinking about FizzBuzz than I do anywhere else.
If I didn't have the modulo operator, I would just check whether division resulted in a round number. I wouldn't rate someone who understands this basic principle lower than someone who just happens to know about the modulo operator.
Bonus points if you use Python and demonstrate that you know the difference between the / operator and the // operator. That's much more useful in day-to-day work.
It's worth noting that the original FizzBuzz problem is not "given a number n, print..." but rather "for the first 100 natural numbers, print...". In this formulation, you don't need the modulo operator: you just initialize two counters at 3 and 5, respectively, decrement them each time, and react when either or both reach 0.
It’s not a trick question nor does it require memorization or study to prepare. You’re not being given 20 minutes to solve something that requires knowledge of an algorithm that researchers worked on for decades that you’ve either practiced or will stumble through deriving from first principles—you’re writing a very simplistic function.