A new study finds that it takes about 50 hours of interaction to move from acquaintance to casual friend, about 90 hours to move from casual friend to friend, and more than 200 hours to qualify as a best friend. How people spent their time and what they talked about affected how close they became.

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A new study finds that it takes about 50 hours of interaction to move from acquaintance to casual friend, about 90 hours to move from casual friend to friend, and more than 200 hours to qualify as a best friend. How people spent their time and what they talked about affected how close they became.