Topic: Data Science.
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Objective: At a party, everyone shook hands with everybody else. There were 66 handshakes. How many people were at the party?
Short Answer: 12 people.
Since everyone shook hands with everybody else, let's assume there are n + 1 people.
Where n is the number of people
n * (n + 1)/2 = 66
n = 12
So there were 12 people at the party.