How to Multiply by 11 in Your Head

The question, solved step by step

43 x 11 = ?

Split the two digits of 43: a 4 and a 3.
Add them: 4 + 3 = 7.
Put the sum between the digits: 4, 7, 3.
Read the answer: 473.
Practice: 52 x 11 is 5, then 5 + 2 = 7, then 2, so 572.

Answer

43 x 11 = 473

The common mistake

Forgetting to carry when the digits add to 10 or more. For 78 x 11, 7 + 8 = 15, so the answer is not 7158. Carry the 1: 7 + 1 = 8, then 5, then 8, so 858.

Parent tip

Let your child check the trick the long way once: 43 x 10 = 430, plus 43 is 473. Seeing why it works makes it stick better than memorizing it.

Video transcript

0:00Can you do forty-three times eleven in one second?

0:07Here's the trick. Split the four and the three.

0:10Add them. Four plus three is seven. Put the seven in the middle!

0:14Four hundred seventy-three! Now you try fifty-two times eleven. Comment your answer!

Questions parents ask

What is the trick for multiplying by 11?

For a two-digit number, split the digits, add them, and write the sum in the middle. For 43 x 11, add 4 + 3 = 7 and write 4, 7, 3 to get 473. If the sum is 10 or more, carry the 1 to the first digit.

How do you multiply 52 x 11 in your head?

Split the 5 and the 2, add them to get 7, and put the 7 between them: 572. You can check it with 52 x 10 = 520, plus 52 more, which also gives 572. This is the practice question from the video.

What if the digits add up to more than 9, like 78 x 11?

Carry the 1. Add 7 + 8 = 15, write the 5 in the middle, and add the 1 to the first digit: 7 + 1 = 8. The answer is 858. Without the carry you would get a wrong answer like 7158.

Why does the multiply by 11 trick work?

Because 11 is 10 + 1. So 43 x 11 = 43 x 10 + 43 = 430 + 43 = 473. Adding 430 and 43 puts the 4 and the 3 at the ends, and the digits 3 + 4 land in the middle, which is why the sum appears there.

How to multiply by 11 in your head