Convergent Science support engineer/application interview questions

I applied online at the end of December and got replied quickly within several days to select a time for the phone interview. The interview took around half an hour with the form unrelated to your own research. Instead, it covers questions such as numerical methods, a 1-D fluid problem to describe governing equations and how to simplify terms, compressible flow, probability, etc., which recalled me of my PhD prelim-exam. My performance was not bad in my mind. However, the result after about 10 days made me disappointed.

Phoe interview was setup. The person speaking was friendly. He explained the answers the if I admitted that I didn't know the answer. I'm writing this part to just fill up the 30-word limit.