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74 Speed Math for Kids
If the answer is correct, the answers will be the same or have a
diff erence of 11 or of a multiple of 11, such as 22, 33, 44 or 55.
Both added to 6, so our answer is correct. Th is is also a test to see if
a number can be evenly divided by 11.
Let’s check the second problem:
0 471 × 11
51181
X X
Add the digits with the X under them:
5 + 8 = 13
Add the digits without the X:
1 + 1 = 2
To fi nd the diff erence between 13 and 2, we take the smaller number
from the larger number:
13 – 2 = 11
If the diff erence is 0, 11, 22, 33, 44, 55, 66, etc., then the answer is
correct. We have a diff erence of 11, so our answer is correct.
Note to parents and teachers
I often ask students in my classes to make up their own
numbers to multiply by 11 and see how big a difference
they can get. The larger the number they are multiplying,
the greater the difference is likely to be. Let your students
try for a new record.
Children will multiply a 700-digit number by 11 in their
attempt to set a new record. While they are trying for a
new world record, they are improving their basic addition
skills and checking their work as they go.