The 11x Magic Shortcut! ✨

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

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

The Trick

To multiply a 2-digit number $AB$ by 11: 1. Write down the first digit ($A$). 2. Calculate the sum of the digits ($A+B$). 3. Write down the second digit ($B$). 4. If $A+B$ is a single digit, your answer is $A(A+B)B$. 5. If $A+B$ is a two-digit number (e.g., $13$), keep its unit digit in the middle and carry over its tens digit to $A$. So the answer is $(A+\text{carry}) (\text{unit digit}) B$. **Why it works:** A number $AB$ is $10A+B$. $(10A+B) \times 11 = 10A \times 10 + 10A \times 1 + B \times 10 + B \times 1 = 100A + 10A + 10B + B = 100A + 10(A+B) + B$. This shows $A$ in hundreds place, $A+B$ in tens, $B$ in units. Carrying simply handles when $A+B$ is $\geq 10$.

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