Welcome to your interview.
The question is on your right: Handshakes Counting Problem. Take a moment with it first.
Talk your thinking through with me if you like - when you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes). Discussion and graded submissions share your five interviewer interactions, so spend them well.
There were 10 people at the party, each shaking hands with each other once. How many handshakes took place at the party?