Level 1 · Quick Tricks
The Elevens Trick
Multiply any two-digit number by 11 — instantly, in your head — using a single rule you can teach in 30 seconds.
The Core Rule
To multiply a two-digit number by 11, add the two digits together and place their sum between them. The first and last digits stay exactly where they are.
Worked Example — No Carry
35 × 11
- Split the digits: 3 _ 5
- Add them: 3 + 5 = 8
- Place 8 in the middle: 385
The Carry Edge Case
When the digit sum reaches 10 or above, carry the 1 into the hundreds place. Only the units digit of the sum goes in the middle.
Worked Example — With Carry
85 × 11
- Split the digits: 8 _ 5
- Add them: 8 + 5 = 13 ← sum ≥ 10
- Middle digit is 3, carry 1 to the first digit
- First digit: 8 + 1 = 9
- Answer: 935
Why It Works
Multiplying by 11 is the same as multiplying by (10 + 1). So for any two-digit number AB:
AB × 11 = AB × 10 + AB × 1 = A(A+B)B
The hundreds place gets A, the tens place gets A + B, and the units place keeps B. The carry rule handles any overflow naturally.
💡 Teaching Tip
Ask students to call out any two-digit number, then pause dramatically for exactly one second before announcing the answer. The pause makes it look like real calculation — and primes curiosity for the explanation that follows.