The '11x Magic' Shortcut!

Ever wish you could multiply ANY number by 11 in seconds, without a calculator or long multiplication? Get ready to amaze yourself!

Subject: mental-calculation • Classes: 6–12 • Difficulty: basic

The Trick

For a two-digit number, say $AB$, to multiply by 11: 1. Write down the first digit ($A$). 2. Add the two digits ($A + B$). 3. Write down the second digit ($B$). The answer is $A(A+B)B$ (digits concatenated). If $A+B$ is a two-digit number, carry over the tens digit to $A$. \n**Why it works**: Consider $AB \times 11$. This is $(10A + B) \times (10 + 1) = 100A + 10A + 10B + B = 100A + 10(A+B) + B$. This structure directly corresponds to placing the sum of digits in the middle!

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