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LESSON 7 · Mental Math Shortcuts

PAUSE TO THINK

What do you get when you multiply 11 by a single digit?

A repdigit — the same digit written twice

11 x 1 = 11, 11 x 2 = 22, all the way to 11 x 9 = 99. Every single-digit multiple of 11 doubles that digit, because the split-and-add trick simply places the digit beside itself with nothing to carry.

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