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Do it in your head!

Level 2

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

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

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Excel in math and science

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It's hard to learn from lectures and videos

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including olympiad champions, researchers, and professionals.

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by Andrei Golovanov

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