ffirs.indd

112 Speed Math for Kids
plus 1. It is important that you can break up all numbers from 1 to
10 into their basic parts.
2 = 1 + 1
3 = 2 + 1
4 = 2 + 2, 3 + 1
5 = 3 + 2, 4 + 1
6 = 3 + 3, 4 + 2, 5 + 1
7 = 4 + 3, 5 + 2, 6 + 1
8 = 4 + 4, 5 + 3, 6 + 2, 7 + 1
9 = 5 + 4, 6 + 3, 7 + 2, 8 + 1
10 = 5 + 5, 6 + 4, 7 + 3, 8 + 2, 9 + 1
How do you add 8 plus 5? You could add 5 plus 10 and subtract 2.
Or you could add 8 plus 2 to make 10, then add another 3 (to make
up the 5) to give the same answer of 13.
How do you add 7 + 6? Six is 3 + 3. Seven plus 3 is 10, plus the
second 3 is 13.
Note to parents and teachers
Often children are just told, “You simply have to memorize
the answers to 8 plus 5 or 8 plus 4.” And with practice they
will be memorized, but give them a strategy to calculate
the answer in the meantime.
CHECKING ADDITION BY CASTING OUT NINES
Just as we cast out nines to check our answers for multiplication, so
we can use the strategy for checking our addition and subtraction.