At a gathering of 15 people, there are 10 people who all know each other and 5 people who know no one. People who do not know each other shake hands. How many handshakes occur?

Each one of the ten people has to shake hands with all the $20$ other people they don’t know. So $10\cdot20 = 200$. From there, we calculate how many handshakes occurred between the people who don’t know each other. This is simply counting how many ways to choose two people to shake hands from $10$, or $\binom{10}{2} = 45$. Thus the answer is $200 + 45 = \boxed{\textbf{(B)}\ 245}$.

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your anwser would be 10 handshakes please mark brainliest i need it bad

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english, cause i can’t you

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i used the pitagoras theoreme