Easy Math Tricks: Multiplying Double Digits by 11

Everybody has their subjects growing up that are easy and everybody has their subjects that are hard. When I was growing up math came easily to me while I hated Science and English. Some people find math confusing but the great thing about math is there are all kinds of trick you can learn to make math easier, especially math that children will learn early on. This trick will help you learn to multiply by 11.

There are some numbers that are easy to multiply. It's easy to multiple by 2. It's easy to multiple by 10. Most children even learn how to multiply all the single digit numbers with the other single digit numbers. Multiplying by 11 can also be easy when multiplying the single digit numbers, you just put the number twice side by side.

But once you get above 10 your 11 multiplication table can get more difficult. There is actually a very easy trick to learn how to multiply any 2 digit number by 11.

All you have to do is take the double digit number and separate the two numbers by putting a space between the two numbers. After you have separated the two digits in the number with a space you then add the two numbers. After you've added the two numbers you'll put your answer in the space. Let's look at an example.

Choose a double digit number:

63

Separate the two numbers in the double digit number with a space:

6 3

Add the two numbers in the double digit number together:

6 + 3 = 9

Insert the sum of the two digits in the space.

693

Now you have your answer. 63 times 11 equals 693.

Let's try another one

Choose a double digit number:

71

Separate the two numbers in the double digit number with a space:

7 1

Add the two numbers in the double digit number together:

7 + 1 = 8

Insert the sum of the two digits in the space.

781

Now you have your answer. 71 times 11 equals 781

Like many rules there is an exception. Try using this trick with the number 99.

Choose a double digit number:

99

Separate the two numbers in the double digit number with a space:

9 9

Add the two numbers in the double digit number together:

9 + 9 = 18

Insert the sum of the two digits in the space.

9189

Now you have your answer. 99 times 11 equals....9189? That isn't right. The exception to this rule comes when the addition of the two digits results in a double digit number. When this happens you only put the second number in between the two digits and you add the first number in the sum to the first digit. So in 99 times 11 you'll only use the 8 in between the two digits and you'll add the 1 to the first nine. 99 times 11 equals 1089. Let's try another example:

Choose a double digit number:

78

Separate the two numbers in the double digit number with a space:

7 8

Add the two numbers in the double digit number together:

7 + 8 = 15

Put only the second number of the sum in between the two digits:

758

Add the first number of the sum to the first digit:

7 + 1 = 8

Replace the first digit with the new sum:

858

So your answer is 78 times 11 equals 858