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Do it in your head!

Level pending

I have 12345 apples. I eat all but 4321 of them. How many apples do I have left?

\[7024\] \[4321\] \[8024\] \[1234\]

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

Master advanced concepts through explanations,
examples, and problems from the community.

Used and loved by 4 million people

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including olympiad champions, researchers, and professionals.

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by Andrei Golovanov

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