AMC 10 2017a Problem 8

At a gathering of $30$ people, there are $20$ people who all know each other and $10$ people who know no one. People who know each other hug, and people who do not know each other shake hands. How many handshakes occur within the group? $\textbf{(A)}\ 240 \textbf{(B)}\ 245 \textbf{(C)}\ 290 \textbf{(D)}\ 480 \textbf{(E)}\ 490$