The Magical 11x Multiplier!

Tired of long multiplication? What if you could multiply ANY two-digit number by 11 in seconds, without a calculator? Get ready for some mental math magic!

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

The Trick

Want to multiply any two-digit number by 11 super fast? Here's the secret! Take your two-digit number, say $AB$. Separate the digits $A$ and $B$. Now, 'sandwich' their sum $(A+B)$ right in the middle! So, $A(A+B)B$. If the sum $(A+B)$ is 10 or more, carry over the tens digit to $A$. This works because multiplying by 11 is like adding the number to itself shifted one place value: $N \times 11 = N \times (10+1) = (N \times 10) + N$. For a two-digit number $10A+B$, this becomes $(10A+B) \times 10 + (10A+B) = 100A + 10B + 10A + B = 100A + 10(A+B) + B$.

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