A small problem in mathematics

Let's set the number of people who go out for an interview in the company. The number of ways to choose three people from the number of people interviewed is

C3n, the number of ways in which they are employed is C 1n? 2. So the probability that both of them are hired is C 1n? 2C3n .. Solution: Set the number of interviewers to n,

So the probability that both of them will be hired is

C 1n？ 2C3n= 170。

N2 n-420 = 0。 The solution is n=-20 (s) or n = 2 1.

So 2 1 person went to the interview.

So the answer is 2 1.