70 Speed Math for Kids
Th ese calculations are easy to do in your head. If somebody asks you
to multiply 72 by 11, you could immediately say, “Seven hundred
and ninety-two.”
Test you rself
Here are some to try for yourself. Multiply the following
numbers by 11 in your head:
42, 53, 21, 25, 36, 62
The answers are: 462, 583, 231, 275, 396 and 682.
Th ey were easy, weren’t they?
What happens if the digits add to 10 or more? It is not diffi cult—
you simply carry the 1 (tens digit) to the fi rst digit. For example, if
you were multiplying 84 by 11, you would add 8 + 4 = 12, put the
2 between the digits, and add the 1 to the 8 to get 924.
9
84 × 11 = 8 24
If you were asked to multiply 84 by 11 in your head, you would
see that 8 plus 4 is more than 10, so you could add the 1 you are
carrying fi rst and say, “Nine hundred.. .” before you even add 8
plus 4. When you add 8 and 4 to get 12, you take the 2 for the
middle digit, followed by the remaining 4, so you would say “... and
twenty-... four.”
Let’s try another. To multiply 28 by 11, you would add 2 and 8 to get
- You add the carried 1 to the 2 and say, “Th ree hundred and.. .”
Two plus 8 is 10, so the middle digit is 0. Th e fi nal digit remains 8,
so you say, “Th ree hundred and... eight.”
How would we multiply 95 by 11?