The 11x Magic Multiplier

Tired of long multiplication? What if you could multiply ANY two-digit number by 11 in seconds, just by looking at it? Prepare for some mental magic!

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

The Trick

To multiply any two-digit number, say $AB$, by 11: 1. Mentally separate the digits $A$ and $B$. 2. Add them together: $S = A + B$. 3. Place $S$ in between $A$ and $B$. The result is $A S B$. *If $S$ is $\ge 10$, carry over the 'tens' digit of $S$ to $A$. **Why it works:** $11 \times (10A + B) = 110A + 11B = 100A + 10(A+B) + B$. This directly translates to the pattern $A(A+B)B$ in terms of place values.

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