In this interview, you will be given a logic-based problem that involves analyzing a social scenario to deduce a specific numerical conclusion. The setting is a party where you and your roommate are hosting, alongside being joined by 10 other pairs of roommates. During the event, you'll be tasked with determining a particular social interaction metric, given a set of unique conditions regarding handshakes. You'll need to apply logical reasoning and problem-solving skills to understand the pattern of social interactions among attendees. If you need assistance, hints will be provided to guide you. Once you reach a solution, you'll be encouraged to explain your methodology and reasoning. 

Jane Street: Handshakes

Calculate the number of handshakes