The Speedy 11x Multiplier!

Tired of long multiplication? What if you could multiply ANY two-digit number by 11 in seconds, without a calculator?

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

The Trick

To multiply a two-digit number by 11, say $AB$ (where A is the tens digit and B is the units digit), follow these steps: 1. Write down the first digit, $A$. 2. Add the two digits together: $A+B$. 3. Write down the second digit, $B$. 4. If $A+B$ is a single digit, the answer is $A(A+B)B$. 5. If $A+B$ is a two-digit number, place its units digit in the middle and carry over the '1' to the first digit $A$. The answer becomes $(A+1)(\text{units digit of } A+B)B$. This works because $11 \times (10A + B) = 110A + 11B = 100A + 10(A+B) + B$, showing the structure of the digits with carries.

Study More with GyanAI

GyanAI is a free AI tutor for CBSE students. Ask any question for an instant step-by-step answer. Try GyanAI free.