The Super 11x Shortcut!

Ever wish you could multiply numbers by 11 lightning fast, without a calculator? Prepare to amaze yourself with this simple trick!

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

The Trick

To multiply any 2-digit number ($AB$) by 11: 1. Imagine a space between the digits: $A\_B$. 2. Add the two digits together: $A+B$. 3. Place this sum in the space. So, $AB \times 11 = A(A+B)B$. If the sum ($A+B$) is a 2-digit number (e.g., 10 or more), write the units digit in the middle and carry over the tens digit to the first digit ($A$). *Why it works*: $AB \times 11 = (10A+B) \times 11 = 110A + 11B = 100A + 10A + 10B + B = 100A + 10(A+B) + B$. This clearly shows $A$ in the hundreds place, $A+B$ in the tens place, and $B$ in the units place.

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