Exterran Engineer interview questions

First they came to our university to recruit. From there there they called 2 of the approx 10 to come to Houston. After we arrived we were informed that there were 10 of us there from different colleges and only 5 would get a job. The next day they held six 45 min interviews which were pretty straight forward with the exception of one. One they decided to grill you and ask very difficult questions plus complex questions with no right answer.