When making a 1L 1X PBS solution from the stock 10X concentration, how would you do it; which formula would you use?

The interviewer will likely ask a variety of situation-based questions testing your knowledge as well as how you explain your process. In this case, buffers and reagents come at concentrations that may or may not be suitable for direct use. This is a common calculation used on a routine basis as a Microbiologist. Don't ask what PBS is as it's irrelevant to the result and it's a common reagent in most laboratories.