Multiplication Facts - 11s

Don’t let eleven and twelve timetables frighten you. They are full of patterns which make mental math and memorization easier than you think.

Eleven Timetables
Pattern One

The eleven timetables are neat to learn because the products results in a double reflection of the number multiplied by eleven.
11 x 1 =11
11 x 2 = 22
11 x 3 = 33
11 x 4 = 44 . . .11 x 9 = 99

This pattern is true for 11 x 1 through 11 x 9.

Pattern Two

This multiplication pattern and strategy applies to all two digit numbers multiplied by eleven.

11 x 11 = 121
11 x 12 = 132
11 x 13 = 143
11 x 14 = 154
11 x 15 = 165

Did you notice? First, the middle number in the product is the sum of the numbers beside it. Secondly, the outer digits in the product are the second factor. So, the following strategy can apply when multiplying 11 x 11 thru 11 x 99.

Example: 11 x 21 =

Steps:
1. Write the second factor as the product but leave a space between the numbers.11 x 21 = 2 1 (notice the space between the numbers)

2. **Add the digits of the second factor and place the sum between the two numbers in step one. (The second factor is ‘21’, so 2 + 1 = 3;
Thus 11 x 21 = 231.


**When the sum is larger than 9.
Example 11 x 39 =

1. Separate digits of second factor: 11 x 39 = 3 9
2a. Add digits of second factor (3 + 9 =12)
2b. Place the ones digit of the sum in the space, meaning ‘2’ :
2c. Add the tens place digit of the sum,’1’ to the hundred place of the product, ‘3’. Thus, 11 x 39 = 429