The 11x Magic Trick! ✨

Tired of long multiplication? What if you could multiply ANY two-digit number by 11 in your head, almost instantly? Get ready to amaze yourself!

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

The Trick

Here's the secret for multiplying any two-digit number, say $AB$, by 11: 1. Write down the first digit ($A$) and the last digit ($B$) with a space in between: $A\_B$. 2. Add the two digits together: $A+B$. 3. Place this sum in the middle space. * If $A+B$ is a single digit, you're done! The answer is $A(A+B)B$. * If $A+B$ is a two-digit number (e.g., 12), write down the units digit (e.g., 2) in the middle, and *carry over* the tens digit (e.g., 1) to the first digit ($A+1$). **Why it works:** When you multiply $AB$ by 11, it's $(10A+B) \times 11 = 110A + 11B = 100A + 10A + 10B + B = 100A + 10(A+B) + B$. This directly shows the digits $A$, $(A+B)$, and $B$ in their place values.

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