Skill 18A
Doubles Fact Families
 There are 4 choices below.
Which one is a "doubles fact family"?
a.   b.  

4

+ 14

18

  

14

-  4

10

  

12

-  5

7

  

5

+ 12

17

  
c.   d.  

7

+ 7

14

  

14

-  7

7

  

not sure