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Can you shakehands with your friends

Number Theory Level 1

Every body in a room shakehands with every body else. The total number of shakehands is 66. Find the number of persons in the room?

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Excel in math and science

Master concepts by solving fun, challenging problems.

It's hard to learn from lectures and videos

Learn more effectively through short, interactive explorations.

Used and loved by over 6 million people

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including olympiad champions, researchers, and professionals.

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by Harshit Verma

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