Interview questions

When I interviewed there was two questions that stick out in my mind. The first question was how would you introduce rational numbers. I know I answered the question wrong. I just gave the definition. Now I would know what to say ( after teaching for over 30years.. I guess I would know what to say after a few years of experience) the next question has haunted me my entire career.
The interviewer says.. so sq rt of 16 =4 and also sq rt of 16 = -4. So by the transitive postulate 4 = -4. I was in shock. I was thinking, how come that doesn't work. I didn't know what to say and was stumped. They moved onto the next question and I asked them to please go back and explain as I didn't understand how come the property did't hold ( that's what got me the job!)
Well fast forward.. this concept has come up over and over and OVER! ( and I laugh every single time!!!)