Adding and Subtracting Doubles

Remember the related subtraction facts for doubles facts.

1 + 1 = 2 2 – 1 = 1	6 + 6 = 12 12 – 6 = 6
2 + 2 = 4 4 – 2 = 2	7 + 7 = 14 14 – 7 = 7
3 + 3 = 6 6 – 3 = 3	8 + 8 = 16 16 – 8 = 8
4 + 4 = 8 8 – 4 = 4	9 + 9 = 18 18 – 9 = 9
5 + 5 = 10 10 – 5 = 5	10 + 10 = 20 20 – 10 = 10

Let's find difference of 18 and 9.

18 – 9 = ?

Consider the doubles fact:

9 + 9 = 18

Its related subtraction fact is:

18 – 9 = 9

So, the difference of 18 and 9 is 9.