90. Several students went to take a math exam. One student calculated that even if none of them "fail," there could still be 59049 different exam outcomes. How many students were there?
90. Let there be $n$ students. For each of them, there are three possible outcomes of the exam: "satisfactory", "good", and "excellent". Therefore, for $n$ students, we get $3^{n}$ outcomes. We have the equation: $3^{n}=59049$, from which $n=10$.