Do some Excel Work

I usually start with the problem description, then stating the solution as the project. Project architecture, one line intro about all the modules. By this time the interviewer looses interest or very desperate to finish quickly just wants me to jump straight to my module. Listening 2-3 sentences they guess and ask me 2-3 direct technical questions before wrapping up. I find it difficult to answer these questions as, they had not allowed me to fully explain the modules. So I feel they might assume me as a person who has insufficient knowledge about the project or my module