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So many fives

Discrete Mathematics Level 5

How many integers between 1 and 1,000,000 contain the digit 5 at least twice?

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, conceptual quizzes.

Our wiki is made for math and science

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examples, and problems from the community.

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including olympiad champions, researchers, and professionals.

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by edil tizon

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