I just had a first interview (after the 20 min call HR interview) with the "lead data scientist". It was a horrible experience. He came 10 minutes late to the interview with a really bad mic. He told me to introduce myself. After finishing the introduction he moved forward to asking me technical question. (Note that he didn't even ask me anything about myself or to really understand what is my field of knowledge). He asked me about a problem of dimensionality reduction which I replied with PCA, he then required me to state the mathematical model behind it! As i said i did not know it by heart he smiled (this underlooking smile). Anyway he continued asking me about formulas as if I should have known them by heart instead of asking me the logical thinking behind it. Then he finished by asking me and algorithmic question which I replied to knowing I was right. But, as if i should be surprised, he told me I was wrong. So I asked him what is the right answer and he told me I was waiting for you to tell me a "formula". Well sorry if my logical thinking and my right answer is not the formula you had in mind. Thrn he smiled (the same smile as before) and told me that was it and closed!