Multiplication · 4-minute lesson

How to multiply by 11 in your head

A big multiplication problem can become a small addition problem. Start with a two-digit number, then use its digits to build the answer.

Step by step

1. Split the digits

   For 35 × 11, keep 3 on the left and 5 on the right. Leave space for a digit in the middle.

2. Add the neighbors

   Add the two digits: 3 + 5 = 8.

3. Place the result

   Put 8 between 3 and 5 to get 385. Check it: 350 + 35 = 385.

What if the sum is 10 or more?

For 87 × 11, add 8 + 7 = 15. Write 5 in the middle and carry 1 to the left: 8 + 1 = 9. The answer is 957. If that carry makes the left part two digits, keep both: 99 × 11 = 1089.

Why it works

35 × 11 means 35 × (10 + 1), or 350 + 35. The middle digit comes from the two digits that overlap when those numbers are added.

Try it yourself

Work through each example before opening the answers.