What are doubles facts?

As one of the short term goals poster earlier in the week, I'm asking that by Monday, each child has their doubles facts memorized up to 9+9.

Each child should be able to answer the following addition questions fairly quickly: 

1+1
2+2
3+3
4+4
5+5
6+6
7+7
8+8
9+9

If your son or daughter already has them memorized, please begin working on what we call "near doubles" such as 3+4 and 5+6.