The Magic 11x Multiplier!

Ever wish you could multiply any two-digit number by 11 in your head, almost instantly? Get ready to amaze yourself with this quick mental math trick!

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

The Trick

To multiply a two-digit number $AB$ by 11: 1. Sum its digits: $S = A + B$. 2. If $S < 10$, place $S$ between $A$ and $B$. The answer is $ASB$. 3. If $S \ge 10$, place the unit digit of $S$ between $A$ and $B$. Carry over the tens digit of $S$ (which will be 1) and add it to $A$. The answer is $(A+1)(S \pmod{10})B$. WHY it works: $11 \times (10A + B) = 110A + 11B = 100A + 10(A+B) + B$. This shows the hundreds digit is $A$, tens digit is $A+B$, and units digit is $B$. Carry-over logic handles $A+B \ge 10$.

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.